I've run a locked rear in my e21 for the past 5 years with no problem. Cheapest LSD you can get.

It does have a tendency to understeer in the corners a bit, but that is corrected with some throttle (takes a bit of getting used to - not what your brain wants your feet to do). Now I love it. It gets me to get on it earlier out of the corners.

Good Luck with your e21. Fun car. Not the fastest out there, but a lot of fun.

Dave