Re: Don't Leave Your Bike Out In The Rain...
Water coming in to the clutch cover just means that there's a little space for the water to come in near the top of the clutch cover, and no way for it to drain out the bottom. Nothing to do with the air cleaner. The clutch cover and its gasket are just there to keep dirt out, not to keep anything in.
That said, I wouldn't leave an uncovered engine in the rain. Wet plug wires don't like to spark, and HT motors are flaky enough when they're dry. Rain might melt the cheap metal into a puddle.