Need a diagnosis :(

[Unsullied_Spy]

Bigger spur/smaller pinion: More torque, less speed
Smaller spur/bigger pinion: Less torque, more speed

Is the 85 degrees at the heatsink or motor can? At those temps it's possible that the rotor has started to demagnetize. If you unmesh the pinion from the spur and turn the motor by hand is it as stiff as it was when you got it? Motor braking adds heat to your system but with your setup you shouldn't be getting that hot. BL motors can generate too much heat by being under geared as well as over geared, so I'd try gearing down a bit to see if that helps and if not gear up a little to see if that does anything.

It was 85C on the can, didn't bother checking the heat sink. As for the magnets being demagnetized, I hope not as that's why I purchased a Medusa!

The motor feels fine and feels just as hard to turn as when I got it.