The right rear window on my 126 quit. It goes down with the switch about halfway, but will not come back up. If raised manually, it slips down about 2 inches while driving and then stops. It can still be lowered with the switch even after slipping. Does this sound like a regulator problem or a switch problem?

Mine did the same thing and it turned out to be a broken plastic part that holds the window to the sliding arm which conects to your window motor. Take the door trim off and have a look.
If its this its a very cheap part but the part comes with a rivit which makes it hard to fit, I replaced the rivit with a small nut and bolt. Make sure the bolt is short enough or it will cause problems.
Mark