Most guys run with the brushes/commutator super clean, but dry. On occassion, I've added a tiny drop of 5W-30 motor oil for noisy runners.
Many of us use the 5W-20 or -30 motor oil for all lube work. (No grease!) You should pretty much lube any moving parts, with the exception of the e-unit plunger and perhaps the brusher, per comment above. (Though I do sometimes cheat there, as noted.)