Creativepunka could be on the right track. A stuffed LSD will act just like a open diff. I had this problem when the axles were cut too long for my R31 diff and the LSD that has been in my brother's Fiat for the past five years is starting to get tired and open wheel regulary. Have you had a look at the centre yet?

I have dealt with alot of people on this site ,both as a buyer and a seller, and every transaction has gone smoothly. Generally I think the vast majority of people are honest but there are always one or two bad apples unfortunately.
Matty