Correctly cleaning (including scrubbing the chamber with a chamber brush and CLP by hand) and correctly upper receiver bearing area lubing with CLP goes a long way.
Same goes for some mags when even brand new, since pulling them all the way apart and cleaning them with CLP can solve some follower binding problems to the inside of the mag.



As for checking the buffer and tube, just pull all the way back on the charging handle, and confirm that the front face of the bolt is stopping around 1/8" to 1/4" in front of the back of the ejection port window back edge, and during the last inch'ish of the charging handle pull, the tension stays the same (read if last inch is greater in tension, then the spring is coil binding up).


As for Gas issues (leak and binding),
CLP around the gas tube to key, and block to barrel front and back, then using a rubber tube to the end of the gas tube inside the receiver will alllow you to use 100lbs of air pressure to check for leaks here.  On the carrier to key, CLP around the base of the key, then hold the bolt in and use around 100lbs of air pressure directly into the front of the key to check if the key is leaking at the base of it to the carrier.