Oh Dear....
I've just tried driving around and -
All the gears are fine except third. Third gear won't select properly and it keeps popping out. I've tried adjusting the position of the gear stick, but no difference. There's more than enough movement for the stick / selector.
Here's what happens: I select third and it doesn't feel like it's gone all the way in, not like the other gears do. Upon letting out the clutch it lets out a GRIND and the stick flies back.
I've now got to take it all apart again to have a look inside

DAMN.
I've read all I can in other, similar posts and I've come to the conclusion that I may have installed one of the synchro rings incorrectly. But it's weird because I'm quite certain that on the bench the gear was selecting fine by hand after the refitting of the pinion shaft.
Could be a selector rod problem? Dunno. Not too happy now! What a lot of time and effort gone! Hopefully I can get it all out again more quickly.

Alastair