Instead of finding threads I will pose this question. What are the signs of shift linkage going bad. And is there anything preventative to date that I can do?
Usually shifting is generally sloopy or you will feel a miss from 1 to 2. But linkages don't go bad that often. So you need more diagnosis and describe exactly what you feel. It could also be your transmission!
I don't think these linkages can be adjusted and I believe need replacing. Your bike is middle aged (or approaching end of life if you haven't cared for it) so if linkage is bad look into Tcro's linkage as an upgrade (if he still makes them). People seem to like them.
The C-10 linkage is adjustable. There is a threaded rod between the pedal and the shaft coming out of the transmission. Loosen the lock-nuts at the ends and turn the threaded rod to lengthen/shorten as needed.
A lot of slop / play in the stock linkages. Maybe some one has the plans for the upgrade Tcro did. I have it and makes a big difference. Look at the pictures and maybe try and copy it.