There were the wrong type of engine supports fitted to early diesel XMs, supposedly up to Q1 of 1992). The replacement top ones are softer and taller, and have a different shape. In fact, the original ones made the engine sit at an angle (the gearbox end was higher by about 1/3 of an inch). Post-1993 microfiches show this replacement, pre-1993 ones do not. If you buy replacements, check that the salesman is checking the right microfiche or you may get the wrong supports: those for a 2.0 liter gasoline engine. The new supports made such a difference I though I had a different car!
The bottom supports of early engines may have been pressed in at a wrong angle. Citroën will try to sell you the whole aluminium support, not just the press-in rings vulcanised together with rubber. Try Peugeot instead: the same engine support parts appear in the 405 and 605.