Its basically a 1970s citroen car gearbox design with heavier bearings and casings now its hauling your motorhome it needs all the help it can get.
Isn't yours a 2004 in which case I'm fairly sure it doesn't have bronze syncros anyway.
Well I sent a message to Mannol in germany an old lubricants company who sell a synthetic gl5 at a very good price
Yes m8 it needs help especially now that its at 160ps
While I have your attention, I didn't know it was an old Citroèn design and at some point there was a mod done to overcome the lubrication problem with the added 5th gear, don't know if you can tell me when this was done? It's just great having an engineer like you to answer questions
Just found this:
I have an Elnagh motorhome on a Fiat Ducato chassis with a 1.9turbo diesel and a 5 speed manual gearbox registered in 2000 (W reg).
In May 2008 I had problems with the gearbox in that the synchro stopped working on 2nd and 3rd gears. I had to have it completely rebuilt with all new gears, shafts and bearings - a new gearbox with the exception of the casing. The problem was that water got into the gearbox via the breather. The company that rebuilt it are gearbox specialists and have had numerous cases of this. They also fitted a Fiat mod to the gearbox breather and I also redirected the windscreen drain away from the top of the gearbox.
Three weeks ago I had the same problem again but only with second gear. Although out of warranty the gearbox company, out of goodwill, agreed to fix the problem if I paid to have the gearbox removed, which I did.
I have now got it back and despite there being no water in the gearbox oil the same problem occurred. Apparantly, It is caused by the coating on the synchro hub coming off. Most gear synchos use steel with a bronze hub but Fiat in their wisdom use steel and steel with a coating of some unknown material which doesn't last. My van in the two years had only done 5900 miles - not very good advertising for Fiat!
Has anyone else had the same problem and does anyone have any advise to avoid this happening in say another 6000 miles. That is apart from the obvious - get rid of it. 90% of motorhomes are now on a Fiat Ducato chassis. Does anyone know if the problem has been designed out of later models?