v50 2 pitted timing cover

Stripping my v50 to try yo work out why I am getting a lot of oil coming out of my timing cover / tacho union and the breather pipe. On cleaning the area around the tacho union I have found an assortment of holes and cavities around the inside of the tube in the casing where the tacho gear assembly goes through the casting. There are also small holes in the flat mating surface where the shoulder of the tacho gear assembly would bed. This looks like air bubbles in the alloy casting. Has anyone else witnessed this sort of thing. On the leaking oil issue I wondered whether the engine is pressurising due to leaky guides or piston rings but compression was good and the leak down test seemed to show reasonable results. Some one has also recently mentioned the breather Air filter assembly and the possibility of blockage or failing ball valve. On a recent run out over about 10 miles there was a fair drip of pale brown creamy oil coming out of the breather pipe under the machine but it wasn’t evident after the return journey. I am quire happy with this assembly as going over to individual air filters seems a little involved. What happens if the ball valve is removed to see whether this is part of the problem? Â