I bought a used reedy 8.5 and it seemed to be fading in the last race. I am running it in a Dex410V3, and they are notorious for hot motors because of how tight the body is, not much room for heat to escape. I did make some cut outs to improve air flow in front of the motor. I am temping 140-150 so that sounds good. Does it really help to put new bearings in, or would it be best to plunk over some money for a new motor? I did not check the esc temp.

Check to see if the previous owner advanced the timing and if it was, back it down a bit. However, most fade in mod racing, especially 4wd mod, is going to be more related to the battery just getting used up hard during a run and should be somewhat expected.

One way to know if it is the battery is to simply drop a fresh pack in and do one or two laps when you notice the fade. Not suggesting two full runs back to back to back without time to cool down. But just as a way to rule things in or out.