I had this problem with my MTH Proto-3 PRR J1 for several years. Needless to say, it was very annoying. The worst experience was when the engine stalled out in the middle of my longest tunnel.
I spoke to the MTH team at the last October York Meet and they sent me several of these collars at no cost. I have yet to try one out, but I am optimistic that at long last there is a solution.