so i'm going to point out the 500 lb gorilla in the room...
whoever you bought that upper from is an idiot. plain and simple.
the fact that they epoxy'ed the handguard on before confirming the barrel nut was properly torqued... i mean wow.
and thats simply based on the fact that i can envision a world where some brilliant marketing team would convince an ar-gunplumber that gluing your handguard in place is a logical thing to do. at one of the hotter points of a firearm. with an adhesive that starts to break down somewhere around 600*F, give or take....
i hope there was at least some attempt at logic like "well at least the gas tube will prevent the barrel nut from spinning off and keep the barrel from falling out" *derp*
in all seriousness....
to start, throw that hot mess of a handguard/barrel nut out and start fresh, and you're right on track about rebuilding it - if for no other reason than to confirm that the rest of the parts he installed are properly assembled.
its just not worth giving it a good solid once over to make sure something else isnt going to come back to bite you in the rear at some point in the future.
i hope you at least got a really good deal on that upper.
here's to hoping that the barrel turns out to be a shooter. 
