It is possible that the plastic guides on your lift arm track are worn beyond their porpose. most likely the one that has a thin slot that rides the edge of the track. (this is the one that controls vertical alignment) the other guide wraps around the other edge and holds the arm close to the track. You might pull the panel on the other door and compare the wear on the arm guides. I have no fix for these two plastic (nylon) guide pieces. If you cannot make your own, you may have to buy a complete regulator to get those pieces.
http://www.vehicross.info/gallery/da.../P10100071.JPG
Sorry it's not a very good picture.