I'm a bit late to the thread but after 20 years of flawless operation my 4 speed overdrive, aluminum case, started to stick in fourth gear, as described at the start of this thread. I removed the tranny from the car and found that for some reason 4th gear was traveling over the normal stop position and causing the slider block to **** upward preventing the gear to move back into neutral. After following this thread and similar I got fed up with trying to identify the problem and moved on to correcting the situation. I build up the backside of the interlock lever (welded a bead about an 1/8 inch) and relieved the front side ( ground out a equal amount of material in front) effectively moving the gear forward. This allowed the slider gear to move into fourth but prevented it from going to far. I bench tested until I got it correct. I installed in the car and have many hours and miles on the car with perfect operation - no issues, works great. I figured 4th gear is the least pounded on gear in the tranny so I had nothing to loose. I know the purest won't like this fix but it works and lets you move on to enjoying the car versus trying to figure out where you lost that fraction of an inch. It allows the car to work the way it should. Before this fix I tried, a new fork and new interlock lever with no success.