I have several 814Xs 2-4-2's in my Lionel PRR collection. A very hardy starter set engine.
Check the commutator face. You should see some copper. If not, spray it with contact cleaner and clean the worn brush residue off it.
Lightly oil all the axles with a drop of oil. Especially the places where the motor armature rides. It turns the most. Oil the gear axles. Put some grease on the gears, lightly. Check the rubber tire. If loose or cracked, replace it.
You mentioned the tender circuit board. That is the SOS board. Ensure no metal part of the board can contact the tender frame. Thick doube sided carpet tape can work.
Add about 5-6 drops of smoke fluid.
The two position reverse unit is normally trouble free. The lever on the top is the lockout switch to lock the engine in one direction, either forward or reverse.
You should be good to go.