Well, I can give an update on this myself. I figured out that in macro mode you are not supposed to be able to use focus (left/right) at all - it is only push and pull. That pretty much told me that the lens was busted because I couldn't get out of macro mode, but I could focus left/right at the same time.
Since it was a fairly cheap lense I figured I'd take it apart to see if it was something I could fix. Turns out that two of the plastic guides that run in the grooves in the barrel had broken (see image). The small pieces where keeping the lens from coming out of macro mode, and the play introduced by the missing plastic parts made it possible to use the focus.
I had another Adaptall lens (80-210) that was pretty bad so I figured that I could cannibalize it and hopefully I'd be able to find the pieces I needed. Turns out that the diameter of the ones in the other lens were approx. 0.75 mm too small, so even if it works there is still an undesirable amount of play in the push/pull action.
Does anyone have an idea where I could get these parts?