i have a 325 tds and also had issues with the car starting, it took ages to get going once it was running it would loose power and at times would cut out whilst at speed.
I had 3 garages look at the car, glow plugs were changed, fuel filter was changed, no holes in any pipes and all pumps were pumping,
after many tests they now feel the cars DDE control unit is broken as wont speak to the obd reader it keeps crashing it or kicking them out.
have you had that checked at all?
I am still trying to find a new DDE control unit as i dont want to pay £1400 for a new one, but have been told i can get one from another m51 engine car and it should work fine, just having trouble finding one lol.