Well the clutch fluild was the first thing I checked. It wasn't load, but it wasn't at max either. I went ahead and topped it off anyway. I couldn't find any leaks anywhere. I donno how air would get in there all of the sudden though. I don't think it's my tranny. It's a low mileage S5 which shifted wonderfully just a few hundred miles ago. It also shifts just fine when the engine is not running... :-/

bleed the line, dont' just top it up