Reading this list and watching those who take it as gospel has been entertaining.
The milspec standards were created by a bunch of ordnance officers who sat in a small room with an M16 and tried to figure out every possible way the rifle could fail and how to prevent it. There is nothing built by milspec that is guaranteed not to fail any more than a non-milspec is guaranteed to be a timebomb waiting to blow up.
I've yet to see any non-milspec bolt or barrel fail unless it was some sort of kaboom involved. This includes DCM across the course rifles that get up to 5,000-7,000 rounds/yr through them in all kind of locations and conditions. Is this combat conditions? No, but it's the closest example of hard use from non-milspec rifles.
I don't count kabooms, as every KB I've seen has been bad ammo and that will disassemble any rifle with extreme prejudice.
It's gonna take a lot of alcohol to convince me that the color of the extractor spring spacer means a damn thing.
I'd never have an M16 carrier on a civilian rifle, at least until there is some consistency in BATFE regulations.
A bolt carrier key should be staked IMHO. One probably won't come apart if torqued down well and red Loc Tite applied, but staking it leaves nothing to chance. With that said, that job's easily done yourself and it doesn't take much of a stake to guarantee that it ain't going anywhere.
I've never seen a loose FSB, period. Parkerizing under it is a red herring. I've seen plenty of M16's and M4's serving GI's in parts unknown missing most of the finish off the barrels and anodizing off the receivers yet the .gov didn't stop the war to refinish them.
Again, much ado about nothing, unless you're planning your own personal war and then I'd say you've got bigger issues to deal with.