We have been using a fuel with rust inhibitor in the fuel and always run the engines dry while warm at the end of a race meet and never in the last 5 years have we had to put and after run oil at all....
I have seen that happen as well the silicon expand and it was from washing in the internals in a wash trough then dried, its like the silicon absorbs the solvents like a kid with a lolly has to have it...lol