personally I think that's absolutely BS
LMT gets away with alot of this as well, every single lower / upper I have has some QC machining marks etc. Everyone says its fine and excuses it, probably how they get away with this bs in the first place.. actually it IS, how they get away with it.
Have them send you a new one, thats ridiculous..
Imagine buying a new house, jewelry, piano, car or boat / vehicle and its all jacked up and its expected for you to just take it..