Rebuilding the flow distributor
Put the distributor unit flat on a surface, so that the side with the two conduit sockets points upwards and the pressure adjustment screw (between two plugs on the side of the unit) is to the right, the side with the three conduit sockets will point downwards then.
Take out the top right plug, followed by the bottom left one. For each plug, you have to press it in (expect quite a lot of resistance) and while holding it depressed, get the retaining spring on the inner side of the opening out. The plug will hardly come out more than a few millimeters but as there is a spring behind it, you can bounce the plug inwards and let it pop out by itself. It may take several tries. And when it does come out, be prepared for a rather strong spring to follow it. Be sure to have the whole unit thoroughly cleaned before you start, using a small brass brush on the plugs and spraying it with a rust remover or screw loosener—any debris along the edge of the plug will prevent it from coming out.
Go on with the top left plug and remove its retaining spring as well. Then, using a blunt pin or bolt, push the piston inwards, on the side where the strong spring came out. The top piston will pop out the other end, pushing out the top left plug as well. Then comes the real problem part, getting the bottom piston out. The easiest way to accomplish this is to use compressed air. Using a hex key, unscrew the retainer found in the bottom right conduit socket (on the side with the three conduits, closest to the pressure setting screw).
There are a restrictor washer and a small plastic filter beneath it. The filters—there are two of them inside the unit—will usually be damaged thus you have to use the new ones coming in the repair kit. Clean the hole with compressed air, plugging the adjacent one with your finger. You could use some cleaning fluid as well, including even water, but in this case you have to dismantle and dry thoroughly everything to avoid damage.
The pressure will slowly push the lower piston out through the hole opened when you removed the bottom left plug and the spring behind it. The best way is to give it a couple of blasts rather than a continuous flow because that will dislodge the bottom piston, which is frequently barely able to move due to the crud deposits.
After having done that, turn the unit so that the conduit hole you removed the filter from faces down, and tap it on the opposite side. That should dislodge the bottom piston end stop, a small cylinder with slots and holes, which will fall out the hole where the filter was in. Once you have done that, you may push in the right bottom plug, take out the retaining spring and then push the plug out by inserting a blunt object through the hole where the bottom piston came out from. Do not try to push the bottom piston out through with the bottom right plug end, as the hole is not finished to the right tolerance beyond the end stop, so you will be damaging the piston pushing it through that way.
You can now remove the second filter from the top right conduit socket (the side of the unit with two conduits, nearest to the pressure control screw), using a hex key to remove the retaining nut inside the hole.
Mark the relative position of the pressure control screw and its collar. Then loosen the collar, but not more than about a quarter to half turn. Now you can unscrew the screw together with the collar on it, do not remove the collar as that will upset the relative positions. There is a spring, a plunger and a ball in the hole that you will be opening. On later units, you cannot gain access to the screw, because it's covered by a pressed-in plug. If you find one, leave it alone. Besides, you can skip this whole paragraph, this part of the distributor is unlikely to have any deposits.
Carefully wash all the pieces. Pay particular attention to removing dirt and rust from the inner walls of the openings the four plugs go into. When you are done, douse everything liberally with fresh LHM to prevent rust formation.
The repair kit contains four new o-rings (don't even think about reusing the old ones, they will leak) and two new filters.
Examine the pistons carefully. If they are shiny on one side but dull on the other, it might be time for a new flow distributor, because this condition means uneven wear—they will never seal properly again. However, experience has shown that this is not a big problem. In some cases the power steering pressure will have to be adjusted slightly higher to compensate for internal leaks in the distributor.
Examine the perpendicular holes at the end of the pistons. If you look into them, you will find a screw with a hexagonal hole. You can use a hex key to unscrew the screw. Between this item and the rest of the piston body is a thin restrictor washer. There are two possible problems here: the screws can be extremely hard to unscrew. The way to do it is to insert a hard pin through the hole in the piston and use a long-end high quality hex key (looks like an L with both legs of equal length). Keeping the piston in screw loosener liquid overnight may be a good idea. The pins used must be round and unbendable. Of course, you never want to put the piston itself into vise clamps or something like that—the surface of the piston is very hard, but it must not be damaged or you can throw the whole thing away.
A more serious problem can be that debris in the LHM, and the disintegrating pieces of the two small plastic filters can blow out the restrictor washers which are quite thin. Look at them carefully, the typical problem is that there will be cracks from the hole in the middle, going outwards. In really bad cases a whole section will be missing. In any case, these need to be in good condition or the flow distributor will not work properly. If they are damaged, they need to be replaced. As far as I know they cannot be purchased separately, you have to take them out of a replacement unit.
If you plan on making one good unit out of several, never mix up the pistons and the body. One set of pistons always goes with the body they were found in. Choose the body and pistons where the pistons show the least wear (they are not shiny but very smooth and slightly dull).
Re-assembly is, as usual, in the reverse order, except that the end-stop for the bottom piston and the filters and retaining nuts and restrictor go in first. Then goes the pressure valve with its ball, plunger, spring and screw with collar. The plunger goes short end in, long end with spring out. Remember to return the screw and collar to their proper places. The screw is turned in as far as it needs to go, then the collar is tightened while keeping the screw immovable with a hex key (steering assistance increases by screwing the screw in, decreases by loosening it—tamper with it at your own risk!). Then come the pistons: the long (top) one goes in so that the end with the spring is to the right, the other end with the restrictor to the left. The short (bottom) piston goes with the restrictor in, spring out. Do not mix the springs for the two pistons and the pressure screw!
Now come the plugs. Put on the new o-rings, push them in and latch in the retaining springs. You'll have fun with the ones with the spring behind, but that's life. The bottom right one will go in deep and of course will not come out because there is no opposing force—that is, until the pressure pushes it out. Even so, do not push it inwards too much, just enough to put in the retaining spring. Put in all new conduit gaskets if at all possible.