Boing is right. The humility gremlins come and get you.
The tube did not actually break, here is what happened: The L1a1 gas tube threads into the gas block, it is not totally fixed, but rather it is able to rotate a small bit. There is a pin under the gas regulator that goes through the block and rides on a flat part of the gas tube threads. This pin keeps the tube from rotating out of the block.
I had the gun refinished not to long before the big match. Apparently the pin was not reinserted into the gas block. So I was using a rifle for a couple of months with no pin in the gas block. However I never had a problem as the tube was still in the block and I never noticed that you could move it more than you should have been able to by hand. (How often do you guys remove your handguards?)
So if you remember my post after it went south at the match, I originally thought it was an ammo problem, because when I pulled off the handguards there was a ton of fouling inside them. I did not catch that the tube was unthreaded, (touch it, it wiggles, ok its good). Turns out that the tube was bouncing around unsecured at the block the whole time. By the time that I got to the malfunction junction stage it had worked its way out enough that I was not venting enough gas to the bolt.
Never trust that somebody else put your gun back together correctly.
The forward assist would have helped a couple of times as the bolt travelled back with enough pressure to extract, eject, and partially strip another round, then it would peter out. So to clear I would have to pull back the handle enough to let if fly forward and push the fresh cartridge in. If you were not careful you could pull it back to far and end up trying to double feed the gun. With a forward assist I could have just pushed the round into the chamber manually.
So I should not have said it broke, more like a stupidity enduced malfunction that cost me big time.