A while ago i had some probs with the gears and the synchromesh. For my own knowledge, can anyone shed some light on:
1) is it really problematic in the 147s
It can be, there have been various parts of the gear linkage,lever assembly, etc that have proven susceptible to early failure, this can then result in sticky gears and subsequent damage to the gearbox.
2) is it easy/costly to replace
Not if you diagnose it early and have it fixed, some of the parts have been redesigned to eradicate the failures.
3) how tight should the gears be once worn in?
I had a second hand gearbox fitted to mine about a month ago, I don't know how many miles it had done but it was about a million times more tighter than my old one. It should have a little play and the gears should select cleanly with a slight pause as you passover neutral, don't try to force it as this can stress the selection system.
4) what exactly is causes gear problems?
Premature failure of gearbox selector plate (seizure then stress fracture of the bolt holding it together), bushes can wear in the both the gearstick housing and somewhere between the selector and the linkages. Linkages can also be damaged by a combination of any of the above.
This then can cause gearstick to stick in 3rd-4th gear, forcing it out then causes syncro sleeve damage and you end up with a gearbox rebuild or in my case a new gearbox as particles had fallen into the gearbox oil and ground away at the selector shaft housing which is a light alloy.
Hope this answers your questions.
P.S This is what I ended up having done.
New (to me) gearbox
New 3rd gear selector shaft
New Selector thingy (can't remember name)