We only got rid of our last one in 2009 (new caravan a bit too heavy), and never had a problem with parts. X-Part are the official suppliers, and as most Main Stealerships were hopeless (I couldn't convince them that my diesel had a cruise control!), but persistence and teaching them to count to 5 and to learn A, B, C, usually got a result. However, there are a number of other suppliers, the best I found was Rimmer's at Lincoln, and I even got the occasional bit from BMW (many of the 75's bits have the BMW badge and part number on them). The only problem with the latter was that it usually meant double the price for the same part!
I would agree with the previous post. The 1.8 petrol is prone to head gasket failure, and is pretty gutless for towing. The 1.8 turbo has more go, but again, that head gasket. The 2.0 and 2.5 V6's are very smooth, but quite thirsty. Strangely, the 2.5 is the better of the two, and has more go. The diesel, IMHO is by far the best for longevity, economy, and probably towing. It also has a chain driven cam shaft, so no belts to change (or snap!), unlike the petrol versions.