I’ve had ARs, M-4 and M-16s as well, that received little TLC and also ran fine. I’ve run them throught the mud and sand and pure salt water and would trust my life to them.
I dragged the M-16 threw about 300 yards of sand in boot camp and learned that if I didn’t want it to jam to keep the ejection port closed. So now I have the habbit of closing it after firing. Better safe then dead.