I had the same problem,with my 84 300d, left side rear did the same thing. I found the fix in the forum and did the same thing. I took out the window regulator assembly as a unit, found the 2 teeth at the end of the regulator gear had worn down. Cleaned it up and had a friend touch it with a mig welder and the took it back to my bench and filed the new welds to look like teeth and it came out perfect and it worked well, save your money and do the same thing, when you find out the price of the unit you be glad you did.

Peter