Thanks for the awesome help everyone here has given me!
I went and bought a 2-pack of propane, and sure enough it is much heavier and my gun is working once again. I feel like such an idiot for not doing this from the beginning, but after reading numerous articles that MAC-11's are really troublesome, the fact that air still comes out of the tank, and how I've only used it not more than 30 magazine fills - my idiocy
may be justified, lol.
At least through this mess, I was able to learn how to take every single part on the gun apart and understand how everything works to avoid a future problem.