I was cleaning my Bushmaster A3 carbine after firing about 300 rounds of factory (Federal) ammo over the weekend and noticed there was a fair amount of fouling around the barrel at the rear ring of the front sight assembly.  It didn't seem too bad, but there was enough that I had to scrub a little to remove all of it.  It was also on the base of the assembly itself.

The gun functioned fine (actually, it's never malfunctioned), so I'm not overly worried about this, but I am curious if there's a small gas leak from the gas tube in the tower, or if there's a leak at the gas port on the barrel/sight assembly.

Answers/fixes I've received so far include removing the gas tube pin and reinstalling the gas tube with a drop of Loctite (from Bushmaster's customer service dept. and from another forum), or returning the barrelled upper to for warranty repair (also from Bushmaster, if it's not the tube but a problem with the gas port), or just leaving it alone, since this is not really a problem and just happens as an AR is shot frequently (from a guy I know who works at Doublestar).  Unfortualtely, all are reliable sources, so I thought I'd try here for some further guidance.

The gun is a little less than four years old with about 2,500-3,000 rounds through it.  I clean after every trip to the range, and hadn't noticed this until this weekend.

So... should I bother with this at all?  If so, in your experience which is the likely source, and is there a method of determining that source?

Thanks for your input.

Slight leak in your Gas block.  Not uncommon.  Mine does the same thing.  Leave it alone .  

Thanks.  It didn't seem to be a problem, but it never hurts to ask.

I've tried to read all of the various manuals and other documents provided by the forum, but (and this is a compliment to the administrators/moderators) there's so much to read that I guess I haven't goten to that yet.  Also some of the links (like the one Dano523 provided) won't open for me.  I think it's a browser issue.

Anyway, thanks, again, guys.

I have a CMMG upper 14.5" and I get the same thing. Alittle bit of fouling around the fron sight but the rifle shoots 100%. Never had a problem with it so I leave it be, however I am thinking of swapping out my FSB for a YHM folding front sight/gas block assembly.