My 16 year old son and I bought a rebuilt 12A engine for our '79 1st generation and about a month later, the engine engine locked up while I was driving at about 5,000 RPM in third gear. We sent it back to the vendor who told us the fixed gear had failed catastrophically and that since this is caused by high RPM (8-9,000) it wasn't covered by the two-year warrantee. I'm asking for anyone who's had gear failures to let me know the cause because my son swares he never took it into the red zone (7,000 RPM). We've already bought a replacement engine, and he really has no reason to be untruthful at this point. It's hard for me to believe that no manufacturing defect or assembly problems can cause a gear tooth to fail resulting in the same locked engine.