I don't think it's the limited slip additive that is the problem but the greater amount of extreme pressure additives in the GL-5 gear lube over what is in the the GL-4 gear lube. The extreme pressure additives are a concentration of active and inactive sulfurs which can react to copper and copper alloys, brass and bronze. There are GL-5 gear lubes with no limited slip additive as well as GL-5 lubes that do have limited slip additives. They both contain the sulfur which is bad for "yellow" gear boxes. "Yellow" gear boxes have copper and copper alloys in the syncros, other gearboxes have no copper, bronze or brass in the syncros and can use different lube than the yellow boxes. Limited slip additive is supposed to be a mixture of friction modifiers including Liquid Wax Ester. There are limited slip differentials that use copper alloys in the clutches, putting high sulfur lube in those diffs wouldn't help the clutch pacs at all.

According to the Society of Automobile Engineers Paper 2007-1-1988 - fully formulated API GL-5 is unable to fulfill the lubrication requirements of limited slip differentials. Some makers of GL-5 add limited slip additive to their lube others don't. I bought three quarts of Pennzoil lube off the shelf at the local garage, two had the limited slip additive one didn't

In my opinion, one should check the API rating, if it isn't GL-4 don't put in your muncie, if it's GL-5 whether it has limited slip additive or not, don't put in your Muncie.