they are asking for the number so they can bring your car up on there computer, obviously this is no good as yours is a 2.0 and your after a 2.5 part. i presume your talking about the bellows, i wasnt aware that there were 3 diferent types though
The auto and manual have different ones for sure. The auto has an extra elbow which goes the the valve-y gubbins and the brake servo. I'm not sure about the third though. I know that GSF supply the manual one but not the auto one, and they probably won't charge you a supplement if you return it. If you have a manual car start there.
I just ordered a new one from the stealers Ԛ£12 + VAT.
They gave me the wrong one to start with as the bloke didn't take my reg number. Mine is a 325 manual. The first one I got didn't have the extra pipe coming from it that goes to the brake servo etc.
The part number for the correct one I got a few days later is:
B13.71.1.708.800
Hope that helps
If you are in the dealers they should be able to bring a diagram of the parts up on the monitor
We fitted a 325 tb on celv's (e30-320i) 320, it was tight but we got the bellows over by leaving it in hot water for a while and then pulling it over with two screwdrivers, (kinda like doing a bike tyre when you were kids!) he said he still wants a 325 one as it is tight, but had no probs so far!!!