Timing Advance Solenoid
This is a typical problem with CAV DPS/DPC fuel pumps. The fuel leaks along the edge of the solenoid housing (a round part with a huge nut on its housing, screwed into the side of the pump). Remove it by unscrewing it with the appropriate wrench, having unplugged the electrics first, of course. The leak develops where the back of the solenoid is joined with the rest of the body, and the replacement is very expensive (cca 160 Euros).
Alternatively, you can use fuel resistant, two-component epoxy resin to seal the leak by applying it where the back plate and body join. I used UHU endfest 300, this glue needs to be heated to achieve optimal curing, when heated it also becomes very watery which seals the crack well. The parts need to be cleaned thoroughly from anything greasy before the application of the glue, which is a challenge considering it's doused with diesel fuel.