How many rounds have the guns fired? The statement "they haven't had any problems the way they are" makes me believe that live fire training is minimal. We had a group show up with Bushmasters at a three day, 1200 round training course a few years ago. Of the six guns, all six had the castle nuts come loose and four had the gas keys work loose during the first day. One of our armorers performed the repairs IG suggested and the officers were able to finish the course.
These are not modifications as others said, they are repairs bringing the firearms up to acceptable standard. The manufacturers that build unfinished substandard guns should get a kick in the ass. Your best bet is getting your PO Colt rifle accepted for duty use. Good luck.

