Long story short, my "new" colt 20" A2 upper needs a new gas tube. I know how to install it, but are there any "adjustments" required to the gas port or hole on the tube? Any heads up on where to get one? Thanks

The gas tube is a rather simple replacement.  No adjustments to the gas port required, just tap out the gas tube roll pin and pull the tube.  The only real 'adjustment' is to be sure the carrier gas key isn't binding on the new tube restricting BC motion and causing wear on the key and new tube.  Some tubes are fouled/carboned in and more difficult to remove from the FSB so you may find it helpful to put a few drops of CLP or Kroil around the gas tube in the FSB and let it sit muzzle down for a day before you pull it...

One source for the new tube is ADCO, another would be Bushmaster...

www.adcofirearms.com

www.bushmaster.com

Ordered one from RB precision today. I got the old one out, but the end was bent. I thought I only pulled straight back, but maybe not. Heated it up and tried to straighten it, but I broke it. New upper from a gun show, and the barrel was loose. In fact, once I removed the gas tube, I removed the barrel with no tools! Easily. Thanks for the reply.

Whoah!

No tools?  Who assembled the upper?  The gas tube is supposed to help prevent  the barrel nut from rotating but you need  a bare minimum of torque on it to begin with.

It was supposed to be a new, factory colt upper. Has CMP markings on everything. All the parts appeared new.  Hopefully the guy I bought it from will be at the next fun show. It is (was) my first AR, and I just got anxious. I also never thought to see if the barrel was tight! Live and learn. Other than an $8 gas tube, no appearent harm. And I got to learn a lot!