I was surfing the 'net looking for prices on rear wiper motors to replace my frozen one. They run about $175. Meh, don't need a rear wiper that bad.
Anyway I came across a couple of YouTube videos where the rear motor is opened up and is completely rusted inside. I figured it wouldn't hurt to check it out. Very easy to remove. Sure enough the inside linkage was very rusted and locked up. The motor brushes were also jammed back into the holders. Pulled it apart and cleaned out all the old grease and rust. Freed up the linkage and brushes. Behind the gear there is a sliding contact/switch assembly. Cleaned it up and put dielectric silicone grease on this part and standard grease on the gear and linkage.
The most difficult part of reassembly was getting the commutator past the brushes.Ended up slipping a wire tie to hold back one brush while retracting the other with a pin.
The results were OK. The motor works but the arm makes a half swipe then waits to complete. I guess my cleaning attempt on the slip ring was not sufficient.
It does work enough for now which is awesome and saved $$.
I have a new tailgate latch on order so when that is replaced I will pull out the wiper motor and sand down the slip ring and contacts and maybe bend the contacts up a little.
It was worth the minimal effort to get it going again.

 

It takes even less effort to search car-parts.com where they run as little as $25+shipping. That's how I replaced mine.

 

I considered used but at this stage I’m concerned if it would be worn out.
anyway the slip ring cleaned itself off after leaving the wiper on for a while so this project is done!!

 

Good job in stripping and cleaning the motor, when you install the new latch mechanism, lube/clean the motor and electrical well again to keep away the gremlins.
Thank for the update.

 

I bought a used one from a salvage company two years ago and it's worked perfectly ever since. Most of them will give you a short warranty.