My experience is that the layshaft is typically the main weakpoint, all are now well worn where they run on the two bushes (yes incl the blind one) and that is a key area to address. The layshaft likely to need dressing at the blind end and bushes made to suit. I normally entrust this to my engineer as beyond my capability (sticking the bits together).
I have a good supply of used dogs and shafts if you need any. Mike Reilly up in QLD should have new dogs and shafts.
These boxes are tough as, so if you get the layshaft running nicely; issues typically limited to whine where the dogs have wear and popping out of gear... ditto but different parts of the dogs.
Good points raised re kickstart gear on layshaft, they are usually stuffed but readily accessible and can be done without a full box strip. That gear doesnt get splash so worth greasing.
