I was told about a 763 used to maintain an employee park at an insurance group. The problem is that they don't know why it leaves black tire tracks all over their concrete surfaces, It's used to smooth the baseball field clay and around the wooded area to remove debris thrown from the highway and for clearing out weeds from around the lake. Machine starts with difficulty then runs fine, doesn't seem to pull to one side or the other, but tires wear out every few months and the black marks are very noticeable. I tried it out myself and all seems normal but going in a straight line with a load of dirt it leaves black tire tracks on the concrete. Of course all around the grounds there's torn up grass too, but I think it's from their young and crazy operators. What could cause a machine to wear down tires when going straight, when everything on the Bobcat looks normal, and the chains seem normal and not stretched? The machine ls also quite rusty and scratched for a 1994 model. It sits outside behind the storage building. I was thinking of making an offer for this thing. Any ideas?