My gas trimmer Model 358.795521 has stopped "trimming". The trimmer head doesn't rotate when motor is running and trigger is activated. The trimmer head can be spun by hand which probably means it is not in contact with the trimmer shaft. I have removed the trimmer shaft from the motor and pulled the shaft from the housing. It is not broken and appears to be undamaged. Both ends look good, no indication of either being stripped or rounded. When trying to insert the shaft back into the housing at the trimmer head or bottom, it doesn't insert all the way. That leaves about one inch extended at the top of the shaft which I think should be flush with the top of the housing. Since the housing is recessed into the motor which would still allow the shaft to contact the upper joint to connect properly. I'm not sure if the problem isn't the gear box itself? Any suggestions?