[Model flyer]

You don't have to replace the motors. Strip and clean them only takes a short while. Once you have the motors out ,two in each lock bend open the tabs that hold the end cover and brushes in place . Be careful not to damage them . The inside of the motors will probably be covered in the lock lubricant. Wash off the grease with white spirit or electrical cleaner,and clean the commutator with very fine wet and dry paper (2000 grit). To reassemble brushes can be held back with a couple of pins through two small holes in the backplate. Once backplate is in position remove the pins allowing the brushes to contact the commutator.