Rear cowl intermittent

[Nick Bailey]

My rear cowl flaps have been staying open on intermittent occasions. When the toggle switch is placed up, to open, the annunciator/light immediately lights like it does as if the cowls have reached fully closed and limit switch stops the motor. Flaps never stick closed, only open. Then the next time I fly, they will close normally when the toggle is placed up to the closed position. On next cycle, they always open but may not close again. Next flight, they might not close when initially prompted, but then at end of flight, close as normal. This intermittent pattern is same flying or on ground with only master on, so I don't suspect a voltage or mechanical problem. Could this be the limit switch, or the motor? I have checked and cleaned wiring as best without removing motor. Motor appears clean at least exterior. My mechanic suspects worn motor brushes. But why does stop limit light come on immediately? Any advice appreciated.