I have an 03 YZ450F with about 100 hours on it and it just popped the head gasket. Otherwise it was still running fine. At this point what should I do to it to fix it? A local dealer told me to rebuild the whole motor but a friend says to replace the piston and rings, and keep riding it. It's ridden at a MX track by a vet rider. I've had it since new and have maintained it well. Thanks.