[LONGHAIR]

The real issue here is that you are not allowing "incoming" air. You have the oil filler tube connected to vacuum, which will produce a vacuum inside the crank case. If you do not have some kind of filtered way to let air in, it will suck in a gasket somewhere. Must likely it will be one of the intake end seals or valve cover gaskets.
The whole point of the PVC system is that it does indeed draw out fumes, but it has another tube connected to the air cleaner to allow air in from the other side. That's the bigger heater hose sized tube that goes to the stock air cleaner housing. Most times when the stock unit is removed, a simple vent is installed in place of that tube.

If you want to keep the valve covers un-touched, you are going to have to find an alternative way to let air in. You could drill and tap a hole near the back of the intake manifold, behind the runners, that would get to the lifter valley. This would allow you to put a hose on it, allowing a "remote" breather. It's not an ideal thing because the intake air and PVC draw would both be in the lifter valley. It probably wouldn't pull fumes from the valve covers as well as the "correct" set-up, but it will eliminate the gasket sucking problem.