I have a MG PRR M1 and a USH PRR M1a that I double-head to pull my 30 car (Atlas) coal train on my club layout which for now is straight DC. Several years ago, I re-motored both using Pittman 9234 BB motors. Recently while pulling my coal drag, the MG model started to run intermittently causing me to think that a tender wheel cleaning was in order especially considering that the MG tender has 33% fewer wheels to conduct electricity compared to the USH tender which was running well. Also, the USH headlight was steady most of the time while the MG headlight was not steady. (Yes, I like my 12v bulbs.) Cleaned wheels on both engines and tenders with little discernible difference. Still convinced the problem was in the MG tender, I removed the trucks, noticed corrosion on bare brass bolster and insulated washer that it contacts. Removed corrosion with a file and reassembled. Problem solved. Question: Should I use a conductive grease or oil where the insulated tender pick-up washer meets the bare-brass span bolster to reduce corrosion issues? What do you use?