As much as I'm enjoying seeing the results of this test I can't help but think that it's a bit circumstantial because of the duration of exposure to the fluids. On long trips I use petrol because that's all I have. But it's only on there for a minute to get the gunk off and I lube it with thick truck gear box oil (the thickest I can find). Usually at night when making camp to let it soak in all night. I check for cracks in the seals as well.
On the next trip I'll be taking terpentine to clean the air filter. Might use that depending on how easy I can find it. I like the idea of WD40 because that's everywhere, but like someone mentioned. It's a penetrant.