I think the key point here is that the foil/furler won't turn when the engagement pin is pulled. That, in my opinion excludes the gearbox & motor. Before doing anyrhing else, go up the mast and look to verify something ( a mis-led halyard etc) isn't binding at the head. You have focused your trouble shooting on only 1/2 of the system, check out what, if anything, is going on at the top of the system. Just a thought. Sincerely, Gary Silver SM 335