The GM-90 engines come with two crankcase ventilation devices, the standard reed valve on the crankcase door, and a regular PCV valve. The PCV has a drilled and tapped 1/2" hole in the top left side of the crankcase, a street 90, and a 1/2" pipe extending to the head level. The PCV valve is screwed into the top of this pipe and has a breather on it. The 6-16 hp models are free standing, and the 20/1 model has the PCV piped to the intake manifold. I've never seen any vapor coming from either device. It does work well to hold a partial vacuum in the crankcase. In any case, it doesn't leak. If someone will send me an email about how to post photos I'll post some.
Mike Montieth