Thanks Martin but the bike is an SP1000 that has been a bloke's regular commuter for ten years. The box has previously been taken apart by someone who didn't know what they were doing, little things like the selector drum shim at the back being next to the drum rather than the pin retainer washer and the gallons of red Loctite on everything. Input shaft peg nut has been well hammered, multiple times by the look of it! The whole thing was probably very 'How's yer father?' Before the spring went.
To my mind the cost of repairing such a massively damaged assembly simply isn't worth it. Can it be done? Of course it can, but it would need every bearing in the box, fifth gear pair, output shaft, any other pinions that are damaged and if you replace them they will be noisy on the old clustershaft, spring, collets, retainer cap, the list goes on. It was obvious the moment I pulled the speedo drive out and it came out covered in silver 'Paste' that what was inside was going to be really, really ugly, I haven't even bothered looking at stuff like selector forks, what's the point? Even if it was rebuilt it would still contain some thirty five year old parts. Who knows how long they are likely to last before wear or fatigue finally take their toll?
Parts alone would be hugely expensive. Instead I buy Joe's box with a genuine sub-2,000 miles and old mate starts off with what is effectively a brand new gearbox, every piece, for about the cost of a fifth gear pair and shock absorber spring. To me this makes much more sense and will be cheaper for the customer.
If you want pics I can take some, it really ain't a pretty sight.