Interesting that you saw more uniform plug colour. There are a couple of benefits that have been pointed out to me in this thread that I was not aware of. Longer valve job life and plug colour.
Yes the small 1/8 inch hole drilled into the pipe plugs that are threaded into the block are to prevent an air lock. That is also why I had cometic add the small 1/8 hole in the gasket to match with the hole in the plug. I was very impressed with the help I received from Cometic gasket. It was my first time dealing with them and they really can make a custom gasket for very reasonable cost.
