After going through several different mag well blocks, I have settled on the ASA system. It goes in from the top and is clamped in place by the upper. It can't move. Once the ejector is adjusted a little, it is very dependable. The only flaw is it's inability to activate the bolt stop, and I have modified mine so it does.
As far as the "badge of honor" on the shoulder, I took a round toothpick and broke it off in the little hole. No more grease spots on the shirt and many, many rounds later the rifle still hasn't faltered in .223, 7.62X39, .300 Whisper, 9mm or .22 LR. The hole in the buttstock screw is a drain hole for water. The earliest AR-15s didn't even have them, as illustrated on page 75 of "The Black Rifle" by Stevens and Ezell. Since I don't invade many beaches or ford rivers with my 16, I feel safe in blocking it off.