I have 10 Vietnam-era M16s with OEM BCGs that are not nib coated, chromed, np3, etc. they are stock, they are dirty and get wiped down every now and then. i drop some lube on them once a month (they sit in the cars all the time) and all rifles have been functioning perfectly. semi auto and full auto.
how clean do you want your BCG? clean enough to eat off of?
it's a work rifle, i don't need it to shine.
i'd buy more ammo.
but in the end, it's your money.