Just started to rehab a 1950s set of Lionel O-gauge trains that have been in boxes for more than 25 years.  I have 3 engines, all of which need lubrication and cleaning, but I'm slowly getting there...they run in the meantime, but not great.  One of them suddenly started reversing direction on its own...change in polarity somewhere along the line?...without my manually having it change direction via the transformer switch.  I can't figure this out...once it gets to a certain point on the track, it will reverse for a few lengths of track, then go forward again, then back over and over.  Any suggestions on how to diagnose and possibly fix this?

Thanks.