James, they are really crappy things the Seuthe units, (yes, even the German's make crap) and unpredictable. They will sometimes stop working even with only using Williams fluid. I think the secret is just a few drops, don't put too much in, it will stop fore sure. I have a few Williams scale Hudsons, and love their heft, I have replaced the smoke in a couple of them with a modified Lionel unit which really pumps it out.
In answer to your question, JY's Megasteam works, but don't mix it with other stuff.