1989 Ford 460 (7.5L) Question

My 460 engine is losing about a quart & a half of oil about every 100 miles it is driven. It is not burning oil and there is not a drop of oil on my driveway where my motorhome is parked. Although... there is oil on top of the valve cover edges and on top of the motor (read further). After a long drive (around 100 miles), when I park the motor home you can smell burnt oil type fumes. It was recommended to me that it may be the lifter cover gasets need replaced. When I took off the engine cover, it appears the oil is actually being forced out of the PCV valve's rubber gasket, and the oil fill hole's rubber gasket. The lifter cover gaskets

do not appear to be leaking.
When I top off the oil to normal levels, the oil pressure is good (slightly high actually). But over the course of a 100 mile drive, the oil pressure gradually goes down until your start hearing that tapping noise from low oil levels.
Any idea's what would be causing the motor to force the oil out like that?

Thank you!
-Chris