My 2008 990S has dirty throttle bodies as well. I keep the valves in spec but they still acquire some varnish (50,000+ miles on the odometer). I think it's normal for these bikes. Possibly due to crank case venting some oil into the airbox?? Not sure, but that would be my guess. Regardless, I wouldn't worry about, check the valves and go from there.
Originally Posted by Newbusa
My 2010R has oil residue on rear throttle body as well and valves in spec.Does not seem to burn oil between changes,I just cleaned it up and re-installed. If it ain't broke don't fix it