OTR

Cold fill machine. We put detergent into a "ball" that goes directly into the drum. The only part of the soap dispenser used is the "softner". Over a few months we get a build up of "black stains in the dispenser and the housing into which it slides. This can be Scrubbed off but its no too easy!! None of our neigbours have the problem!! Any ideas how to cure this ... Thanks in anticipation. Dennis