Hello Kev,
Maybe my friend and co-author Rainer Kleinsteuber can help you with your problem with your contact brush.
Rainer developped a whole new concept brush including a stainless steel brush.
See attached chapter 4.2 of our book "Our Model Garden Railway"(see Amazon)
He takes orders for all types of locomotives.
He has 40 years of experience improving G-scale locomotives.
His native language is German but he speaks Dutch very well.
Thats why he wrote the German issue of our book.
Should you have problems in contacting him in the English language I'm very willing to help you .
His mail is :
rainer.kleinsteuber@gmail.com
My mail is :
glm@vanderschrieck.nl