Hi Roger, for the drip feed oilers of the Gemini, steam oil is probably too thick. Use a thin machine oil of good quality.
I generally use steam oil to lubricate all parts of an engine unless very delicate drip feed oilers are present, which require a thin oil.
Regarding dirt etc: if there is a lot of hardened oil and dirt on your engine it means it hasn't been cleaned for many years. Hardened oil could be present inside the cylinders too and make the engine turn with difficulty. I recently bought a Hemmens engine in this state and here's what I did: I have repeatedly dripped thin oil inside the intake pipe, then manually turned the flywheel until it came out of the exhaust and the engine turned freely. This will dissolve the old oil.
To clean the engine exterior of hardened oil, thin oil is very suitable. If very stubborn try alcohol. Be careful with other solvents as they can attack the paint.
Anyway, you should make a habit of wiping off excess oil from your engine after each run, that way it won't attract dust.