When the Dover Composite was put into service, the Brush was a National SA-45, they ran great with no issues. Then Dover changed to what they called the super brush. I can't remember who the manufacturer was, but they worked well also. When ever you change from either of those 2 brushes, you will invariably have compounding issues. That said, the advice about the the stretch of the selector cable is very true. One other thing I have encountered is the brake drop relay hanging in with residual, and the R C circuit that is in the brake drop, can also give you a compounding look. Last but not least the brake core itself may need a good cleaning. A quick check to see if it is the brake, is to put some pressure on the brake shoes, holding them together with your hands. If the car stops level you need to look at the above.