The gear will come out in this fashion along with the shaft when you hammer.
Here the gear and rod have come all the way out (just pull it out). Notice the dark bands on the rod, that's the problem area. Clean the rod with carb/choke cleaner and use a metal brush.
Corrosion on the rod also indicates corrosion on the inside of the shaft housing. There should be a small black o-ring on the inside end of the cone, save it so you can compare at your hardware store to get a new one. Use a metal brush to thoroughly clean the inside of the cone (yes I had a heck of a time pulling that brush in and out of the cone). JF member ZJfreek suggests using a 9mm (or .38spl /.357mag) barrel brush to clean out the shaft.
Pull out the brush and spray down the inside of the housing with carb/choke cleaner and make sure all metal shavings/dust/dirt have been removed. Roll up some paper towels and pull them through to ensure a clean inside.
Using a flathead or knife, apply a large wad of grease on the inside of the hole in the housing. I would recommend a silicon or very wash out resistant grease in this application. Then take the rod lightly cover it in grease and push it all the way through and wipe off the excess.
Before you push the rod all the way to the end, ensure that it spins with little friction when it is almost entirely in the housing. This was the whole purpose of the project. Now push the gear all the way down and MAKE SURE IT IS IN THE ORIGINAL POSITION that you marked earlier (didn't you?). Notice in this pic the brass faceplate on the gear is missing. Don't make the mistake of removing it like I did.
Take the circuit board and lightly apply dielectric grease to the four pins mentioned earlier. DO NOT BEND THEM DOWN or they will no longer make proper contact with the brass plate on the gear.
Lastly, apply dielectric grease to the brass plate and the yellow gear to reduce corrosion and wear, respectively.
Put the gear cover back on, carefully snap the circuit board back on and touch the motor contacts with a soldering iron again to resolder the connections and put the circuit board cover back on. Don't forget about the rod o-ring and o-ring retainer. Apply grease to the o-ring and slip it over the end of the rod, then put the o-ring retainer on the end and push it down until it's snug against the housing. It's important to note that if your new o-ring is rubber then you should not use a petroleum based grease as they swell rubber, use silicone grease instead. Conversely, if your new o-ring is silicone then use a petroleum based grease instead of silicone.
Reinstall the completed motor and enjoy!
Forum member Inavacuum
also posted a good point.
"I did exactly what the thread says to do and mine is working great. I also added a step, I resealed the outer little rubber grommet with some silicone putty stuff to prevent it from happening again."
JF member cyberbonga states that the hatch must be closed before testing the motor otherwise the wiper arm will only sweep halfway.