Help!

Just had my 85 Westy worked on and my mechanic cleaned and greased the shift
assembly, but he said the guides were too worn and should be
replaced/rebuilt(too much play in the shifter, sometimes hard to get into
gear, reverse is the worst). Van has 135k.  Could someone shed some light on
this problem?  Replace, rebuild kit, how to etc. 
Thanks,

Bill Lund