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A general service? I don 't think there's anything serviceable in them, in that the bearings are sealed and don't require re-greasing, and the brushes last the life of the armature. I think it has been discussed here before that there is a difficulty in sourcing components for the Mitsubishi unit like the Solenoid and the contacts, so run it 'til it dies and buy another.
If you just want to take it apart to clean out mud or seaweed, then carry out the usual procedure as you've described above.
