Yeah, syncros still worked, it was jumping out of 3rd gear, chap was told it would need a new match pair 3rd gear set, which also includes 3/4 syncro assy, so he got the parts, then asked me to take box apart and fit them. So I discover that he had previously "rebuilt the box" last year, but it still jumped out of gear, hmmmmm.
Worrying thing, is that once in bits, I could not find a convincing reason for it jumping out of 3rd on over run, some very minor wear on the teeth, and a small amount of slop on the layshaft 3rd gear set, but nothing that would convince me it was the reason for the issue, it all measured up ok as it was.
Well we are this far into it, lets put the bits in and measure their backlash, end float etc, all within specs, so a good clean up of gasket surfaces, and put back together.
All gears worked, all worked as it should, but little voice in the back of my head still wanted to find the reason why it was doing this in the first place.
Nothing obvious like a spun mainshaft bush under the gear set, excessive backlash, or obvious wear on the gear teeth, detent all worked ok, no wear on the selector forks or shafts, correct alignment etc.
it all checked out.
Hmmm