The Marvel oil or any light viscosity oil or trasmission fluid might help. I have done that soak down many times on all sorts of engines and never seen any damage done. The usual procedure has been to remove all the plugs, pour several ounces of oil into each cylinder, lay a shop rag loosely over the plug hole to catch the excess and turn the harmonic balancer a few revolutions. Whenever putting an engine away for the winter or longer I do that. There’s a smokey startup but that’s no big deal. Isn’t 500,000 miles pushing the limits on that little engine.