Selector spring
Make sure that the spring ends on the two shifting positions (forward = downshifting and backward = up-shifting) are always in contact with the selector plate
Make sure that the clearance between the end of the spring on the selector plate and the stop pin is almost null, when in home position (see diagrams)
Pawl
Make sure that both pawl tips run free, without jamming.
Selector plate spring
With a thickness gauge, check that the spring is not deformed by over-stretching.
See also specifications for this operation.