K&N had a "bad" batch of filters in the last year or two. Moto America had a "ban" on aftermarket filters for a while...may still? The o ring surface was slightly smaller in diameter than it should be and resulted in leaks. Only saw one personally, but it did end a guys trackday, but luckily he and others didnt crash from the leak. Make sure to compare it to the one you remove and to the other 2. Other problems come from the nut, but those are user induced!
Brad, Suwanee Ga.
'09 V650, several others too!