Unless the OEM starter is rotten... normally all you have to do is to disassemble it, clean everything, use some 600 grit sand paper on the commutator, use a small screwdriver to scrap the junk out from between the copper plates of the commutator, and replace the brushes.
It takes more time to pull it out, and reinstall it that to do the rebuild.
Back in the day... Gokey (sp?) starters were great. Now it seems like all the after market stuff kind of sux.