kingjbh;
It sounds like the mesh is off. Minimum space between the gears without binding is what you need. In all the Years that I've owned HPI's, I think I've only had to replace 2 gears, one from pebble damage and the other from a broken 2spd shaft.
If the One-Way is bad, the car will not run at all. The tranny will just slip. Put a small dab of grease on the inside of the One-Way bearing every couple of weeks/races.