a. Bent shift fork, moving a sliding gear or sliding dog too far in one direction and not far enough in the other.

b. Shift drum shimmed too far in one direction, causing the sliding gears and dogs to move too far in one direction and not far enough in the other.  Correct by moving the shims from one end to the other until engagement is correct in all gear positions.

c. Main shaft shimmed too far in one direction, causing its sliding gear and dog to engage too far in one direction and not far enough in the other.  Correct by moving the shims until the engagement is correct.

d. Lay shaft shimmed too far in one direction, causing the sliding gear to engage too far in one direction and not far enough in the other.  Correct by moving the shims.  As long as one shim remains on the left end of the lay shaft, all the others can be moved to the right end if necessary.

NOTE: The above examples are extreme ones, except for the bent shift fork.  In normal conditions, the Ossa transmission will not require such drastic changes of shimming, as the shims are very thin and don't normally affect the gear engagement of the transmission.