22G68 box internals remote and magic wand

[65Austin]

Are the internals the same for a 22G68 remote box from a 65 Cooper 998 and a 22G68 magic wand from a 65 850? I am trying to chase a problem on the Cooper; 4th gear pops out on deceleration. I wondered if I can source the needed repair bits from the wand box?
Not sure of what the problem is or what I might need to fix it, I think I have eliminated everything on the outside that I can think of.

[36inter]

Possibility that somone may have left the large circlip out that retains the input shaft bearing, I have seen that happen, then it all moves sideways and you loose 4th gear

Pete

[65Austin]

i can select 4th and it stays when under load and driving, it is when i let off the accelerator to slow down it pops into neutral, all other gears work correctly.