I fixed mine today, and it seems to be working, but it has only been a few hours so far...

I actually read the intro pages in my Haynes manual, and read thru the Chemicals and Lubricants section. It talked about some kind of anaerobic locking compound, which is meant to "lock" something that may later need to be "unlocked" (like a nut).

In the store, I purchased Permatex Threadlocker Blue. A small tube cost about $7. Blue was for medium strength, so I thought I would start there. They also sell a Red for strong, and another for super strong.
I got mine at a Kragan, which is like Autozone or Pep Boys.

On my unit (wiper unit that is), the rubber bushing at the base of the mounting bolt is a bit chewed up. I imagine the previous owner tightened the bolt down to a fault in the past. I simply doused the mounting bolt "cone" with this Blue Threadlocker, and then doused the inner "cone" of the wiper arm, and reinstalled the arm on. Upon tightening the nut all the way down, I was disappointed to see the arm slipped, and I could still move it. I was gonna try a lock washer, but that would not have any affect since the slippage is occuring inside the cone. Nevertheless, I moved the arm into the desired position and hoped for the best.

It was a nice 75 degree Southern California day, and my wife was going out with the car for the day, so I figured this would be a good time for something like this to cure.

Tonight I had the occassion to go out. While turning the wheel or something, I had one of those inadvertant instances where I accidentally hit the wiper lever. Usually I hate this cause it smears dirt across the window, but tonight I smiled as I saw both wipers working. I turned it on full speed against a dry window, and let it go for a minute and to my pleasant surprise, the wiper worked flawlessly. The next rain storm will be a true test, and if I incur a failure, I will report it, but for now it is fixed. Should another failure occur, I will try some sort of pliable or rubber spacer, maybe some kind of thinfoam doublestick tape, in the cone to give it a little something to grip onto a little more since the rubber bushing on mine is thrashed.

Good Luck!
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1995 850T Wagon 101k
1998 V70 GLT Wagon 85k