First off, let me say you get what you pay for, I know that now. I'm some what dissapointed with the gun. I've had problems with the gas systems and its failure to push the bolt back and eject a shell sometimes even when the regulator is at 0.  Well lately I noticed that the gas tube comes loose up by the front sight post and when I make it tight again , the 2 slots that are at the front end don't line up with the holes that are in the regulator, But it throws the emptys out like you would'nt believe, so would it be a good idea to locktite it shut that way so it would not open up again ,or dou you guys see problems with that idea like excessive wear?  Also how accurate  should this gun be, it seems like I can only get 3-4 inch grouping at about 60 yards with a scope, I'm using FN and IMI ammo from the early 70's.  If the barrel was not torqued enough the groupings would be worse than that right?

Is the receiver an IMBEL?  If so, the best thing to do is to send it off to Derek Huffman (assuming he is still doing it), and get his Century Rebuild Special (I believe it was under $200, including a nice refinish--makes the sow's ear into a silk purse).  

Then you should have no further problems, AND have a nice looking gun to boot.

I too once had a L1A1 from Century. It worked ok but it got groups much like you're describing. I got SO sick & !@#$%^&* tired of adjusting the gas regulator every time I switched ammo that I finally sold the GD thing.
Then I bought a G3 parts gun. Voila`! No more adjusting!! It's a recoil operating design: just load and shoot! Makes life much more fun at the range.