I decided to clean a few AR15s due to beer aids and extra time.  

Last time out my Armalite M15T started short cycling.

I cleaned it and found the gas key was poorly staked and had come loose.  

I bet this was a thing with Armalite from that era.  I just didn't catch it on the forums and stake it properly.

Every one I clean, I change to a Colt gold extractor spring with black insert.  I guess I need to do the rest now.

Good time to catch up on gun maintenance

I hear those Colt springs are the gold standard. I’ve only ever wore out 1 extractor spring and replaced it with BCM.

Do you use the Viton o-ring along with the Colt spring and insert?

No need.  That is the purpose of this part.