[1994lt1]

Well I went to Island recently and ran a new personal best of 13.2 at 103.5 mph. When I was getting ready to go the second time I did my burnout in the water and noticed that only one tire was spinning. I ignored it and ran 3 more times. Sometimes both tires would start spinning then as the radials warmed up just one would spin. So I am wondering what my options are at this point. I tried to research it and I've seen that the rear in my car cannot simply be rebuilt? I was thinking of just buying a new Posi unit and throwing it in, but I don't want to do anything before actually knowing what is wrong. Someone told me that if I change the fluid it may cause the clutches to stop slipping internally.

So I pretty much don't know much about rear's at this point but I am learning a lot through research. What do you guys think I should do first?