Slamfire, you are talking about two extreme cases,
The first had to be more then 500 rounds. The second will case the gas plug not to seat and STAY.
Like I said.
Lock the bolt/op rod back. Turn the rifle upside down and back a few times. It the gas piston slides back and forth leave it alone. It it sounds/feels slugish, clean it.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071