Oil coming out of air filter area

I recently started noticing small oil puddles under my engine after riding. I traced the "leak" back to my air filter area (the crankcase exhaust tube?). After doing some research, it appears that "blow-by" can cause this to happen. My bike has 20K miles on it, and it started leaking last fall after I had an 18K mile service performed by a Kawasaki dealer. During the service, they adjusted the valves and, of course, replaced the oil. Has anyone had experience with blow-by, and would changing the oil or adjusting the valves cause this to happen for some reason?

Thanks!