Before spending more on expensive bulbs, test the headlight power leads with a meter while the thing is running and see if it is getting the correct 6V or reasonably close. If it is you can eliminate stator issue and focus on the correct value bulbs. Head and tail are one circuit, brake is a separate circuit with a resistor. The resistor is ONLY for brake light. If one of the head and tail is blown it will take out the other sooner or later. Check BOTH headlight bulb and tail light bulb for correct value.