MY01 Gearbox Issues
 

I have had my MY01 for over three years now, from new, in the last year the gearbox started to crunch between 4/5th, the diff was replaced three months ago, now the box is crunching between 3/4th, but much more noticably. I have sourced the partnering box for the diff and am having Town and County fit it.. they want 713 quid incl vat for the fitting including new flywheel and clutch kit (c/w r.bearing) is this a good deal? am I getting ripped off? what options do I have at the time of replacement for upgrading flywheel etc . I heard that on earlier boxes the crunching can be caused by the retaining nut on the 5th gear coming loose, is this an issue with a newage box ? are they the same ?
Sorry for the the question bombardment but we are talking a few quid here, and I am nervous of the outcome.
Any....ANY input would be appreciated
Thanks
EwanS