I'm guessing the windings or brushes too. I have bad luck with thin wire dual fields on the diesels, not steam though. But overheated eunit fingers might do that too And a shorted smoke unit is a possible draw issue that can be overlooked as heat and smoke isnt that unusual here. (It used to be tinsel, lol, has been a stray wire clipping and a stainless wire wheel bristle loss to date).
Pressure is a big factor questio in electrical contact. The more the better. A weak sprung brush's potential suffers directly proportional to pressure loss, but I've never needed to replace one as weak yet.
After a dressing, new brushes, springs, etc., the commutator may get dirty faster with brush dust, and clog the contact plate gaps quickly, especially if lots of oil is present. It's just part of breakintg them in. I can bush them clean one at a time with a paint brush or toothpick without disassembling on some motors.
The finer the better on sandpaper, clean the brush tubes, wipe brush faces well & dress them flat if you must, &/or watch any slant is at least oriented the same or your pickup timing is off up to near ⅛" too. Isolation and continuity/resistance check on the armature and shaft.
The field can be a PITA. I've been lucky enough to be able to do armature swaps to findout as soon as it warmed it was crap.
