Best cocktail
Have not heard anyone mention PB-Blaster yet? That is the best Penetrating Oil on the market. Does not evaporate right away.
Whatever Penetrating oil you use, give it "Time" to work, days . .
If I ever have to pull off rusty bumper bolts, I start soaking them down with PB-Blaster a week in advance and keep re-appling it to keep it wet.
They come apart nice then when I have a go of it.