If you are dealing with a museum layout, I would expect there'd be some steam? If so, the running gear needs to be lubed, probably about every 10 hours of operation. The gear tower and motor bushings are one thing, and they have been covered. I would not oil the brushes in the motor! They need to be free and clean, but not lubed. Arcing inside will just turn that lube to sludge, then taffy, then enamel. None of which get thumbs up from the engineers who design electric motors.
You can use any light oil that is intended for use with plastics and exposure to paints. Hobbee-lube, Labelle's, are examples. They make greases as well.
I use Dexron III Mercon automatic transmission fluid for my outer wheel bearings and for the pivots in the valve gear, the cross-head guide, and the main and side rod cranks. It is a superior lubricant, most household garages have a near-empty container whose remaining dregs would lube even the largest museum fleet at least once, and it is easily applied. Best yet, it is entirely safe for both paints and plastics. It has to be because it was designed for use inside auto transmissions with plastic-cased sending units.
Invert the locomotive and tender in a soft, but firm cradle designed or fashioned to hold those items well in their inverted states. Then, take a medium-sized sewing needle and jab the pointed end into a short length of wooden dowel...in one end of the dowel. A drop of CA glue would help to keep it there. Then, using flush cutters or sharp wire cutters, nip off the top half of the eye of the needle (close your eyes or turn your head!!). You'll have two small tines showing. Holding this appliance by the dowel handle, you dip the two tines into a thimble-full of ATF fluid, and then apply the tiny drop to the bushings, pivots, and cross-heads. Be methodical so you don't forget one. Work from back to front or the other way...don't jump around because you'll miss something. Also, avoid the tendency to place a second, third, and fourth drop in the same place because you don't see any of it after you withdraw the sewing needle applicator. It doesn't need any more unless you missed!
Last thing is to power the engine and run it for a few seconds. You can do this while it is still inverted by using wires and alligator clips to an axle with pickups. Or, place it on the tracks and run it back and forth for 20 seconds.
Crandell