How can I clean wipers on a Budd (or another locomotive ? )

First, Merry Christmas to everyone !

Now my problem : I have the two Budd's of NH, nr. 31 and 41, I run them together ; the trucks are connected to chassis via black wires, they can be seen from the underside ; the #31 runs fine, but the #41 loses sometimes contact and stalls, the #31 begins to slip. I noticed that the problem comes especially from one truck, if I put the railcar on track with this truck only it has difficulties, and the contact detection is unreliable if this truck is in front, so the double railcar stops too late ; I suspect the wipers, which could have a bad contact due to oxydation. What can I do, without dissassembling the whole engine ? Should I use a "contact spray" which I could apply on the inner side of wheels with a brush (without risk of damaging plastic parts), or is there a special product by Labelle (not the "track conditioner" )? Or should I send the railcar back to HRT and let the "specialists" solve the problem, I am afraid that the problem could perhaps be related with the connection wires ...

Thanks for any answer ...