Use of a good quality synthetic like Mobil-1 or AMSOIL will remove most build-up over time with regular oil & filter changes thanks to their excellent detergent qualities. The amount of "sludge" starting this thread is relatively insignificant compared to that encountered in extreme service environment engines with high mileage and exclusive petroleum lubrication. In that instance a more thorough cleaning of the block and oil galleries can produce enough material to pose a problem to circulation or even blockage.
The area underneath the valve covers is a unique "in engine environment" as the build-up there comes from a combination of oil vapor, oil splash (from valve train) and water vapor produced by normal engine condensation. So what you see there isn't necessarily indicative of what the rest of the engine is like, and being valve covers you can just scrub with a stiff brush and degreaser followed by a good hosing off.
This will be a much more relevant topic for those VX owners not using synthetics as we start getting more machines with 200K miles and higher.![]()