It's actually fairly straightforward. Large e-clip holds the cannon assy into the bushing assy that attaches to both sides of the playfield.

Unscrew the bracket with the motor on the underside of the playfield. A pin running through the motor shaft keys it to the cannon.

Pull said e-clip. Unplug the connectors for the cannon solenoid and switches. Lift assy out top of playfield.

Clean the bushing and the motor shaft with your solvent of choice. Put back together.