Sounds to me like you have a bad motor bearing. Either that or you've overheated the motor pretty badly and ruined the magnets. Either way I'd just get a new motor. Those little 380 brushed ones are cheap as dirt.
It’s a Traxis Titan.
Super affordable, but it required a little excavation in the motor well area.
https://www.amazon.com/Traxxas-Titan-18-Turn-Brushed-Motor/dp/B0027GGZYU
This is everything you'll need. Plus a battery