I wouldn't use it where it could get in the fuel. So I wouldn't use it on the fuel cap O rings or anything like that. I don't know if it is fuel soluable, so it might cause problems in the carburetor or fuel injection system.
It's better known for valve cover gaskets that have a history of weeping, and some have reported that it extends the life and improves the ease of replacement of intake gaskets at the head. A thin application on gaskets for oil strainer or fuel pump to the accessory case, like that.