[BrianG]

Not really. The anodizing on the motor case sometimes can have fine "cracks" if it got too hot, but doesn't necessarily mean it did get too hot. Even a little loss in magnetic strength can result in a substantial loss of performance and increased heat.

Has your runtime decreased lately? If a rotor got partially demagged, you probably have to apply more throttle to retain the same performance, and this should show up as reduced runtime.

What gearing are you using? If you are running on asphalt doing nothing but high speed runs with little stop-and-go, the motor could just be would out and need a little more gearing. If you are doing lots of stop and go (like racing or general bashing), gear down a couple of teeth.