'92legacy

This is a '92 Legacy So my rear diff was smoking/tight all of a sudden and I changed the oil. It was running okay for a couple of days(a little vibration/grinding) and now it is smoking and tight again. There are no visible wet leaks, and there was a good amount of oil left when I changed it. I didn't see very much metal in the used oil, but like I said, there has been some grinding. Do I have to replace the unit? Is there just a gasket I could replace? And how much will it cost? Thanks

I have a '92 Legacy. My rear differential just started smoking and is causing a lot of resistance. Any ideas-is it shot, or is there a way to lube it? And if I can't afford to fix it, is there a way to disconnect it?