Folks, I'm here to bust another of those persistent myths that linger around the world of model railroading. Today's target: "plastic-compatible oil". I've heard this said enough around here recently that this myth deserves to be put to rest, again.
This seems to be another of those claims made by the manufacturers of certain products, which strikes enough fear in the heart of the consumer for them to choose their product over someone else's.
I challenge anyone to find an oil that will actually damage the plastics used in model railroad drives, which are mostly so-called acetal or "engineering" plastic (strictly speaking, polyoxymethylene). This material is by nature resistant to all oils, greases and most solvents except the very strongest (like acetone, MEK, etc.) This stands to reason, since this plastic is formulated for use as gears and cams, which typically need lubrication.
I've used ordinary oil and grease on plastic gears for years with no ill effects. No oil or grease is going to dissolve or break down your Athearn or Kato (or even Overland) gearboxes. (For grease, I keep a can of white lithium wheel bearing grease handy: works like a charm.)
This is not to say that there are better and worse oils: one reason to use expensive oils like LaBelle is that they're purer and cleaner and don't leave residue behind. But you can even use WD-40, if you separate the lighter lubricant from the other ingredients (which do tend to produce gunk after the lubricant evaporates). The key thing is to find an oil that doesn't leave crud when it evaporates, as all oils do eventually.
The moral, once again, is that just because something is produced as an Official Model Railroading product doesn't mean that you can't use a non-offical product with just as good results. And usually for cheaper, too.