blow by is common on alot of motors, ever hear of a pcv valve. that's what it's for. but i agree, it is a common problem on harleys. i've actually seen people put maxi pads in the air cleaner cover to catch it. typically it's just a mist that is supposed to recirculate through the intake.
it's funny though, because harley owners accept these type of problems with thier bikes, and actually will make excuses to make it sound ok. i dunno why.
read any v-twin orientated magazine and you will see all kinds of fix-it articles. the aftermarket makes a killing selling cures for factory defaults.the current major one is a whining noise in fifth gear in the new six speed trannies. there are a ton of complaints about this. a baker upgrade to fix it runs about 900 bucks without labor.
but being a harley mechanic, it keeps me in business. i will never run out of work. ha ha