w8ye is correct, suggestions are endless...

I once let two engines sit about seven years. They were gummed up tight as a drum. I'd run Omega with castor in those engines. I flushed them with Green 15% Cool Power five years ago and never looked back. I've been using 15% Cool Power exclusively with all my 2 and 4 strokes ever since. I don't use after run oil.

At the start of every flying season I open up my radio and check for corrosion, particularly on the little header pins of the circuit board where the battery connector plugs in. I started checking because one year just by total luck I happened to find those circuit board battery connection posts totally corroded to the point where I just touched the plastic connector and the connector fell away from the board. Thank goodness that connector hadn't fallen off the board while flying. Anyway, that's why I now open up my radio and check every year.