On a 1995 525TDS, as the fuel tank level drops below about 1/2 full, and the car is not started for a couple of days, it takes a lot of cranking to start. With a full tank it starts immediately. Is there a "lift pump" on the tank that lifts the fuel and sends it at (? lowish)pressure around a loop ? If so, presumably there is a dip tube which may have a tiny leak, or poor seal, allowing the pump to become "un-primed". There seems to be no fuel leaks anywhere, either after standing or when running (no tell tale signs of leaking fuel on underside of car)
Perhaps this is a typical problem on a "lift pump" of more than a few years old, so is the remedy new seals or is it a case of a new pump assembly ?
Thanks,
Nick