Location, location, location.....If those breathers had been installed on the opposite side of the valve covers, no oil would escape. See the previous photo of the Corvette valve covers. The side mounted oil breathers should always be installed on the intake manifold side (high side) of the valve covers.
When the engine is running, oil is tossed off the rocker arm and onto the exhaust side of the valve covers and then it puddles in the breathers. If you remove the breathers and cover the breather hole in the valve covers with a plate, the fumes and oil will not have any path to escape. Problem solved.