Lionel, at one time, said that only their premium fluid should be used in their Legacy units as the other brands could leave a buildup on the critical smoke unit components. Many have disagreed with that claim, as Nick does, use many different fluids.
I would probably stay within the Lionel Premium and Megasteam fluids for my choices as they seem to be thinner and may be less likely to gum up. Older fluids like SuperSmoke were developed prior to fan driven smoke units and it has a thicker viscosity.
Megasteam makes an "Eliminator" smoke fluid that is intended to remove any residual scent from previous fluid so you can start fresh with a new scent and not have the old and new blend together. The eliminator fluid has a lemon smell to it.
