Took my new to me SAI M1A out today for the first time. It is in a Sage Mod 0 EBR stock, mid nineties vintage rifle. Trouble is it wont pick up a round from the mag when it cycles. Hammer resets but it wont grab a round. Using new CMI mags and DAG surplus. When I got home I discovered a slightly loose gas plug and the piston had oil on it from the previous owner. Could this be the issue? What are possible causes? Ive ruled out ammo and mags since I tried several & they all work great in my Scout. Thanks guys!