ee
That is what was stated in class (from my contemporaneous notes, not memory): standard carbine buffers, Colt action springs and gas rings. Given all the bandwidth prior to that time (July 2006) on heavier buffers and such for short barrels, his statement was noteworthy. (ETA: So I made a note of it. He did not state, nor do I recall anyone asking, how the guns came from the factory. I corroborated this with two other people who were actually there. Could it be that is how they came from the factory? Could they have been purchased some time ago? Since you are talking to Dean, you might ask him.)
I think your recollection on periodicity of checking the gas rings is is faulty. Here is the TM:
TM9-1005-319-23. Check out Section 2-7 dealing with Preventive Maintenance Checks and Services. PM's are Quarterly, not every 3000 rounds. (Crane hasn't finished its shot counter yet.) While a good idea, it requires the user to maintain a gun book. And that notion, also very good, is not a requirement of the TM. So they schedule it quarterly.