Hey Peter,
85A is still very reasonable with the 1513 motor, so I don't think your motor is damaged. I demagnetized a Hacker C50 once, and the motor current went up to about 110A.
I think what's more likely is you don't have enough airflow over the top of the motor. What I have found is that it helps a lot to open up some air holes in the nose of the plane, on top, just behind the spinner. This lets air in directly over the top of the motor where it is most stagnant.
The Sebart Wind S Pro comes from the factory this way, and my motors always run much cooler in this plane.
Unfortunately, the only way that I know of testing rotor magnets is to compare the magnet pull force to a rotor that I know is good. What I do is place each magnet on top of a digital scale that has a metal pan, and then I measure the force required to pull each rotor free from the scale. If the pull force is the same for both rotors, then they are both good.
Brenner ...