I have read about these problems and would only like to make one observation all carry very heavy weight which is unstable at most time. This would put pressure on the clutch, brakes and gearbox.
I have an 03 Trafic (same as Vivaro) and I had a gearbox replaced at 39,000 miles. Lucky it went so soon as it was still under warranty (I bought it at 37,000 miles). The van has now done nearly 90k. The list of issues is screen washer pump around 50k, clutch around 75k (fair enough I suppose) and the slave cylinder tends to be changed with the clutch anyway, steering pump around 50k.
The issue with the gearbox is not about load strain. It's about the gear selection mechanism. Apparently, where the cable enters at the bottom of the gearbox, there is inadequate sealing to stop water getting in. This leads to a bearing becoming corroded and wearing prematurely. Whoever designed it that way wants shooting. I certainly hope they at least got sacked - and I'm normally quite a forgiving person. My understanding is that from around the 55 plate onwards, they were made with more protection to stop water entering. I also notice from the records that the master cylinder on my van was changed before I had it.
I did wonder for a while if I had bought a lemon but since a number of faults occurring, it's not been too bad since. The MOT bill last year was about £300 (including the test) but bits need replacing on steering and suspension from time to time. I accept that as fairly normal wear and tear. It's major parts wearing prematurely due to crap design that I find irritating. It's not as if diesel powered vans are a new concept.
