Sounds like fuel in the plastic air lines to me.
I had this problem until getting the chance to fix last weekend. 6 O-rings will cost around £10 from the dealership.
The problem I had (I had replaced the 3 plastic lines on a previous 320CDI) was disconnecting the lines without breaking the catches, which were brittle due to age.
I broke 2 but I, erm... superglued the pipes back on and they won't come off in a hurry. It was bank holiday Sunday...
Also, I made sure that the fuel filter housing was correctly screwed on.
I put plenty of grease around the thread and tightened as much as I could by hand. 25nm if you have something large enough to grip it.
This problem had been going on for months, especially when cold, and most times it would eventually start by continually cranking for 40-60 seconds, but after calling out the RAC for the second time, I thought I'd better sort it out.
Starts on the button now and its harder to get the ECP warning if I floor the car, because now it receives fuel instead of air and fuel!
If it is the HP pump, you will be able to see or smell diesel. The seals on the pump weep when cold, but re-seal themselves when they get warm.
