With the gearbox on the bench, it’s a quick job to remove the bell housing and expose the ends of the main shaft and lay shaft.
The synchromesh is on the end of the main shaft so it will be easy to diagnose the problem.
First of all the clutch withdrawal mechanism needs to be removed.
I have to remove the selector shaft to remove the synchromesh but all 3 springs are missing. One is lodged in the selector. I think this has caused the jamming.