Solution that came from the customer: "I have several of these nice engines which you can solve the issue of poor connection on a long term base by course filing/cleaning up the Tender wheel axles and the associated brass pickups and then applying a dash of " BURNDY" penetrax copper joint compound. (This is used in the electrical trade for a long term prevention of oxidation build up) Clean up and add the compound and then run the locomotive for a while" - Our customer from Australia