Peter, let me make sure we have your reported problems understood correctly:
Motor 1 won’t work in tender 1/loco 1
Motor 1 itself works ok with direct connection to the brush contacts
Motor 2 works in tender 1/loco 1
Motor 1 won’t work in tender 2/loco 2
Do I have all of that correct? I think that is what you’ve said?
If I do have it correct, there is nothing wrong with motor 1 or tender 1/loco 1. The only thing that can be faulty is in the motor 1 connection to the tender, any tender.
Does that help?