The grease is black or dark green, so I would just re-spread it back on the gears and re-install the cover. Be careful not to get a shaft out of the hole, you can tell this by the cover not going back into place. Patience and care will result in it going back together with no issues. Also the screws holding the end bearing cap can be loosened and the armature re centered in case the problem is due to drag on the motor.
Best of luck with the activity, if it were me I would buy a spare gear motor and have it ready to go, remember these things never quit on the warm days!