Peter,
RE: "The way this smoke unit fills may cause overflows, its kind of a funnel with 2 right angles, so I think the fluid cant pour in smoothly."
Here is an enlarged photo of your GP9 Y-shaped smoke funnel copied from Lionel's parts web site.
It's very similar to the Y-shaped smoke funnel on my Lionel Legacy F7 (6-85206) and I too have had smoke oil wetting the circuit boards in vicinity of the smoke unit. In my diesel engine, the inside top of the engine shell seals against the two Y-funnel holes (see photo above) with a small and very thin gasket compressed between the inside top of the engine shell and the top of the Y-funnel holes shown in photo above. I believe that is a weak point in the design of the smoke oil filling channels. I believe there is smoke oil leakage across the two Y-funnel gaskets when one adds smoke oil through the engine shell 'filler' ports; I doubt that there is a tight seal between inside of engine shell and top of Y-funnel so smoke oil leaks across the gasket into the engine compartment. This leakage is exacerbated by the rather small Y-funnel channels that go from the two filler port entry holes at a very shallow angle and on into the smoke unit reservoir fill hole. These rather small channels coupled with the very shallow fill angle going down to the smoke generator cause resistance to smoke oil passing across the gaskets which leads to leaked oil getting into the engine compartment. I also believe that when the smoke generator is in operation, some of the smoke generator oily smoke passes across the gasket into the engine compartment to some degree thus leading to even more oil-film wetting of engine components like electronic circuit boards. I plan on changing out the two thin Y-funnel-to-engine shell gaskets with homemade thicker gasket materials to ensure leak-proof seal between Y-funnel and inside of engine shell.
Regards,
Tom
