I purchased a 2009 KX 100 for my son 5 days ago. He rode it less than three hours over the course of the five days and it has seized up. The crank rod and bearings are shot. The bike only has 109 hours on it and the top end was rebuilt at 85 hours. The previous owner filled it up with racing fuel but said he also used 40:1 in it as well. It seized up about 30 minutes after we filled it up with a 40:1 ratio 91 octane, no ethanol gasoline. My question is, did the bearings just coincidentally wear out or does it have something to do with changing the fuel? Anything else would make this happen?