I have an opportunity to purchase a 60" Z scag. The owner tells me that the deck belt jumps off the pulleys when the mower is accelerated. He thinks the reason is the deck is bent. I have looked at this mower really well and don't think the deck is bent. The mower runs well and at idle the belt stays on just fine. The shafts look tight and straight. Have any of you had this problem, if so what was the cause?