Lightly grease the wheel bearings and gears. A little bit of grease goes a long way, so don't overdo it. Before you apply new grease, clean off any old grease, especially if it is gummy or hardened or dirty.
A drop or two of oil (not grease) on the motor bearings would be good.
Do not grease the motor brushes or the contact surfaces of the pickups/sliders.
"It is one of the happiest characteristics
of this glorious country that official utterances are invariably
regarded as unanswerable."
-Sir Joseph Porter, First Lord of the Admiralty (HMS Pinafore)