I have an old SD9 that I bought back in the 80's for my old layout. Today I started working on it to prepare it for an LM2S. The first thing I did was remove the wheels and axles, separate them, mount the axle stub in a drill, and polish the treads of the wheels with Flitz polish. Then I also polished the axle end that fits in the truck bushing, and cleaned out the bushing. I did all this to promote better electrical conductivity. The wheels came out looking like new Intermountain wheels, nice and shiny. Then I put together an old Sagami motor and driveline parts to mount to the stock truck drive gears. I also lubed the gears while I had them apart.
As soon as I get my new speakers, I'll see how it works out with the new decoder.