Hi Gary K,
Thanks for the comment. I’d like to think a change of gearbox oil would fix my problem and I might try it this week but somehow I doubt it will be that easy. I have no noises from the gearbox and even if I hold it in 5th manually for a while it will not stay and will jump out immediately. Do you happen to know the name of the garage in Luton? I might call them to see what the likely price would be to fix the problem.
I might also Google some more to see if others have been able to fix this problem just by going a gearbox oil change.
Thanks and I will update people with the outcome soon.
All the best
Gary B