I just picked up an older Mantua 0-4-0 steam loco & tender. I know that they have a reputation for contact issues. It is clean & lightly oiled. It seems to get power from one side on the tender (which has metal wheels) and the opposite side on the loco. It runs smoothly in forward or reverse when the transformer wires are touched to the wheels. On the track it runs really well in reverse but hesitates and struggles forward. Is it related to the connection between the loco & tender (flat piece of stiff plastic)? The tender wheels seem to barely contact the track and when I press down on it the loco spins and wants to take off. Like I said, I am perplexed?