RE: Black goo
Best thing is not to get in the Amsoil trap in the first place.
Saw a friend fall for Amsoil - and then running it richer 80:1 - and then all the black goo - and then he changed to Redline at 50:1 - and he's now happy.
Has taken all flying season for the black to work its way out of the engine/muffler.