There is not really much to re-build in them. Replace the buttons if they are worn, rollers on the arms if they look worn, and a new spring thats not sacked out would help. Check the ramps, they should be fine unless the rollers locked up and wore through the case hardening, then the ramps would look all mushroomed over and worn. Clutch faces can be cleaned up with a scotch brite pad, if your careful, while its running. Inside, belt dust and gunk, just a grease removing type solvent is ok. When done, spray it out with brake cleaner to get any residue left over from getting on the belt.