1. How much do you tighten the gas cylinder plug? If I do not tighten it enough it comes loose during firing. I recently tightened it too much and I ruined it. I was able to get it off and I ordered a new one.

2. The M14 owners guide says to clean the gas system every 300 rounds. My friend has an M1A and says this is BS but he admits he does not shoot his much. I never actually got a manual with my gun and I only have the M14 owners guide. Is this BS?

The gas plug should be turned to hand tight and then tightened 1/2 turn more.  I usually clean the gas cylinder about every 500 rounds and that works for me.

Match rifle shooters clean/decarbon gas system every time they shoot a match.
The amount of carbon build up will be the same, same pressure build up for repetable
performance. gas plug tightening spec. is 15 ft/lb put a paintmark on the plug/gas cylinder
to line up after future cleanings.The threads on the plug are softer the the cylinder and strech on initial torquing repeted/ torquing or over tightening will ruin them.  hope this helps

                                                            Bob