Hi Peter,
I had a similar experience. I had noticed increasing energy consumption during flights, but shrugged it off to windy conditions.
Then I went dead stick, and as I flew directly at myself hoping to make the runway, I saw flames through the chin cowl! The ESC was a lump of charcoal, but fortunately I had it mounted away from the fuse, so it didn't do more than smoke-damage the plane. I can't remember what the motor looked or felt like, but I sent it to Neu and they diagnosed de-magnetization. This is indicative of high temperature in the motor. I do a lot of baffling etc, so not sure what else I could/can do to keep it cool. It's probably a snowball effect: heat causes some demag, which results in more heat, etc. Neu gave me a good deal on replacement and I have hundreds of flights on 2 contra/Neu units without additional issue (of course, a single person's experience proves nothing).
Dan