I have removed the starter motor on my Scrambler 500 and found one of the brushes was very worn. I installed the rebuild kit from my Polaris dealer and the starter motor should be fine.

While I have things apart, I also removed the bendix, or gear drive assembly. My service manual does not give any info about rebuilding the gear drive. It basically looks like a couple of gears and some springs. Has anyone rebuilt one or had to replace anything? It seems to be slow to retract back after I twist it and engage it. For the starter, the service manual says to use silicon based grease to lube the bearing and bushing. Should I use the same thing to lube the bendix?

 

I am in the middle of the very same job with my Sportsman 500. I thought the starter drive was sticking so I pull that off first and I found the same as you that the return spring seemed to be weak. I pulled the drive apart cleaned and regreased the shaft and stretched the spring. Put it back together and it retracks much better now.
My starter problem turned out to be brushes and as you only one seemed to worn but after looking closer it was only stuck down. A littler WD and working it in and out and it was as good as new again........