Kind of a minor issue, but apparently I'm looking for a unicorn.  I have installed 3 gas blocks and 2 tubes and they all leak from the front and/or back of where the tube inserts.  Low profile and rail topped.  Put over 500 rounds through one set and it never sealed.
Is there a way to seal it or find a more matched set?  The gun cycles fine but the stainless barrel gets filthy and inside the front of the handguard is impossible to get clean.
Any suggestions or just "hose it off"?

That's one reason I've been getting black nitrided gas tubes and barrels lately.  Black hides the carbon build up.  I don't think there is any one combination that seals better than another.  I have factory A2 sights as well as low pro gas blocks.  All eventually get dirty over time from the small amount of gas blow by.  It's the nature of the beast.

Carbon on your barrel inside your handguard won't hurt anything. We're dealing with high pressure gas and unsealed fittings. They're going to leak. If you shoot your guns, they're going to get dirty, scratched, etc.

Agreed. I've built 4 dream builds, all with adjustable GB's. 2 from Superlative Arms, 2 from SLR. All clamp on nitride. All use nitride gas tubes. 3 are mid, 1 is carbine length. No matter what, you shoot them, they leak a bit.. even with the gas pressure throttled way down. All function flawless and the tiny amount of leak does not hurt a thing. Does make my OCD go a bit nuts... but whatever.

And like Rkangel777, I found that Faxon nitride barrels hide the dirt better than my SS Odin Works barrel.

Go shoot, have fun, relax.

Rock on,
Jim

The gas key on the carrier gets some sealant so it doesn’t leak. Put some of the same sealant or red loctite around the gas hole in the barrel and it won’t leak. -CB