agro1, Keith, et al,
As noted, crankcase pressure seems to be problematic for these seals. After I had my problem, I had Craig at Top of the Hill build me a breather unit that many of the guys in the Bay Area are running.
Essentially, -12AN bungs are welded into the valve covers (both) and are plumbed via -12 hose to an aluminum breather tank mounted on the firewall. The tank has a drain, and can either be drained back into the motor, or a scavenger of sorts. At the top of the tank is a breather element, and a larger diameter cap that fits down over the element.
It ventilates well and keeps the
oil from blowing out of the breather all over your engine. Looks cool too.
Call Craig at Top Of The Hill - 925-460-5297 and he can set you up.
Brad