You may have a combination of problems.  It is very disconcerting that the motor stalls as it has a great deal of torque.  I would first separate the foil from the gearbox.  This is accomplished by removing the three 10 mm bolts located around the cast aluminum piece riveted to the foil.  You should be able to lift the foil using the genoa halyard and attaching the swivel to the cast piece.  This may take a little persuasion due to corrosion around the shaft.  The foil will move up a few inches and when free of the gearbox you can try to turn the foil.  It should turn freely if the halyard is not so tight that it is jammed at the top.  If it turns freely your problem is in the gearbox or motor.  I would next check the motor.  Remove the motor cover, check the connections at the motor and in the port side front locker.  Check the motor brushes.  You can remove the motor and make sure it's shaft turns freely.  If no problem has been found to this point, the issue must be within the gearbox.  I believe removal has been described in other posts.