Originally Posted by georgesgiralt
On the invoice there is a saying about a couple of modifications on the selection system to make it more reliable.
He's probably talking about the shift kit. It was an upgrade that likely happened right after your bike was made.
As for the sticking shifter, were any of the c-clips hard to reinstall after the springs were changed? I know there is a place in the shift mechanism where there have been two thicknesses of spring: the thicker one binds up on some bikes. I think it's #17 which wouldn't explain the problem fully, but if it were #4 it definitely would.