Hi just reading your thread
If it seems to fall out of gear then that is probably the Detent springs basicly they push ball barings against dips in the selector shafts and provide a possitive lock when you select a gear
You need to remove the floor and the transmission tunnel to get to them
two are held in by the L shaped plates held down with 7/16 nuts and the third is under the big brass bolt between the other two
if it bashes its way out of gear then there is a more serious problem with the gearbox.
been there done that and I still smell of EP90
Dave