Rob, in my opinion no maintenance required unless you're having problems with the motor. See Van's letter titled Flaky Flap Motors, if you haven't already. You can do a search on their site for it. After 10 years of normal operation on my -6, I decided to check the internal condition of the motor IAW this letter. I ended up replacing the brushes and cleaning the commutator (cleaned up the excess grease), otherwise all seemed normal. You can order spare parts from Usher Industries, if necessary. Also, make sure you perform the safety wire mod to the rod end that Van describes in a service letter. There are variations on this mod that involve drilling a small hole through the rod end for the wire that seems to be an improvement on the original mod. There's plenty of information in the archives on this. I would suggest that you also check the entirety of the flap mechanism for any binding that might put unnecessary loads on the motor.
