Splitting, cleaning and re-greasing an EM motor gearbox

Steps

Remove the motor from the game and separate the motor from its gearbox where possible (often two machine screws, except on Multi-Products motors).
Catch the light spring and brass bushing on the armature shaft; they are easy to lose and are essential.
If the gearbox halves are riveted, grind the heads off one side with a rotary tool and drive the rivets out with a punch; some boxes use screws.
Lift off the top half and take the gears out one at a time, photographing or noting the order and position of each.
Clean each gear and both case halves with alcohol.
Re-grease lightly with a Teflon gel lubricant.
Reassemble, using spare EM switch-stack screws and nuts (about #4 size) in place of the rivets.

Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part Two, Clay Harrell (pinrepair.com)