Well, a 242 case is a different animal, and has its own reliability issues regarding the limited slip clutch inside. Personally, I do not think its an improvement, and I would not buy any used 242 case unless I saw it in operation or it came from a reputable parts supplier, with a returns policy.
If you were driving for any length of time with little or no fluid, your case is likely scrap inside. The case uses hundreds of tiny roller bearings which will fail (or become badly worn) very quickly is run with no fluid.
BTW in 2 wheel drive, the chain does not turn when the rear wheels are in the air, so any looseness there would not produce noise in 2wd.
I know this is not what you want to hear, but I think you need another 231 case.