Toy Story woody Lionel train stopped working?

New, Duracell batteries, tested and all good, in remote and train. All lights and sounds work. Control board is clean, welds all seem connected well but I can't see the welds to the motor. Motor functions very slowly at first, but stops and one gear seems locked in place, but I see nothing for it to be locked on. Gears are very well greased and all other gears function as normal. Is it the motor? Or the gear? How do I fix this thing?