The gearbox is simple enough - I just changed rubber seals on my "A" box.
If the bearings are shot - new are very cheap.
A gear set is expensive, but can be bought.
Also rubber seals, gaskets and spring washers.
So what is the problem?
Except the gear set costs €544 + tax (in Sweden).
I guess it's because you want a cheaper option...?
Cheers
Erik