yeah its bizarre. my brother had a hobbit that got left in a damp garage a few yars ago that the crank turned into a solid rusty mass, but nothing else was affected at all .... super odd. usually with the two stroke oil coating things, even setting up, engines tend to stay pretty clean.
i dunno if its more or less common with a dellorto on a shorty intake vs. the stock bendy has anything to do with it? Maybe something with the exhaust? who knows.