I have so far used lacquer thinner, on the advice of the people who make the CMX track cleaning car (brilliant by the way, that beast, but it takes a BIG heavy loco to push it by itself). I have used kerosene on the advice of the people over at MRH who published a comprehensive list of track cleaning possibilities in the way of fluids about 2017 or later. I also liberally applied ATF, Dexron II Mercon, to my rails before I demolished my second layout just for laughs. I had been using the ATF for a lube for my steamers' outer parts, and it works like a hot damn.
I'm happy to say that Dexron II and III varieties don't seem to impeded connectivity, and they also didn't seem to cause slippage under my locomotive when tried it. Since I tore it down two weeks later, I cannot speak to the durability over time.
On that list, kerosene was #1, followed by WD-40 Contact Cleaner and CRC Contact Cleaner and Protectant. That is because they are 'non-polar' fluids which are neutral and don't induce charged dust and carbon particles from arcing to adhere to the surface of the rails. They also minimize exposure to the air, so less oxidation over time. Well down the list were clipper oils and lacquer thinner, and ATF.
I don't know if that is useful, but I can say it didn't seem to hurt. I now use kerosene in my CMX car, and so far it seems to work well. I don't get the sense that the little bit of kerosene left on the rails has damaged any traction tires.
ATF is a synthetic, at least the Dexron varieties are. They are also the AFT designated for use in auto transmissions with plastic sending-unit cases, and I can assure you it is also paints safe.
