Since your the expert joost i don`t dare to disagree, But i just want to share my experience and hopefully it will help oneother. Running 1/12 i had the same problem when i used 2 tracks with balls on the spur. When i changed to one track > problem solved
. Could be that its caused by the way the diff rings are pressed to the balls. It seemed in my case that only one row/cirkel with balls got the pressure from the diffrings wich caused the second row to slip and heat up. Well any way lots of advise i see.
i would say try it and see if it helps you like it helped me.