[ducatimann]

Have you tried turning the motors by hand? A light spray of electrical contact cleaner or a couple drops of lighter fluid on the commutator through the opening in the plastic endbell followed by hand turning may free things up.
Replacement tires can be found online. Ortmann makes urethane tires for these older wheels with the flanges on the outside edges. (modern cars use a center ridge to stabilize the tire)  EJ’s Hobbies is out of business but their tires can be found at online retailers and eBay.
Other more experienced members who are into vintage slot cars will probably chime in soon with more advice, In the meantime, buying a couple new cars will save Christmas for you. ?

I’m being really cautious of the plastic gear on the axle as I don’t want to damage it but it can rotate, just not easily. There is some sort of green corrosion by the gear on the motor. Will try some lighter fluid and see if it works!

I also need to source a new spring for one of the remotes as it was not inside the body of the controller.