I went to get some oil to deaden the growling sound my Atlas engine makes on occasion and they did not have any, but they suggested 3in1 or sewing machine oil. Is this okay or do I really need a particular oil type?

I have Sprectrum cars that weighty more than that new from the box, an example is a single dome car and the triple dome cars. I have several 50' box cars that are much lighter than the Spectrum cars which are maybe 1/4 the weight of the Spectrum cars. They are so sensitive to any difference in track uniformity that it makes them worthless to even try using.

I have several cars of unknown make which are terribly light. I was thinking of opening them and gluing washers in them for extra weight so they tracked better. Does anyone else do this? Any thoughts on this?