Since this post has been tacked for over a decade, still work fine,

http://www.ar15.com/content/page.html?id=122

So short version, pull the old key bolts and throw them away.

Clean both the bottom of the key and its mating surface on top of the carrier with something like acetone/finger nail polish removed from the wife.  Not only will it de-grease the surface, but clean off any residues that my be trapped there where the old bolt snapped as well.

Add a drop of loctite to the top of the carrier where the key will mate to it, drop the carrier key in place with a few up and back strokes to migrate the loctite being used a gasket sealer between the two, then torque the bolts. As for key bolt torque, is has increased with better mil spec bolts and key material over the years, but your still better off with the old spec of 27in lbs (3.7ft lbs of torque) since we don't know the hardness of the key metal/if it has been produced to the harder mill spec of not.  Once you have the key bolts tightened correctly, then blow down the gas tube to migrate any loctite that may have layered over the gas tube passage, out of the passage.

When you go to re-stake the key to lock the bolts in, it's the softer key metal that you want to peen into the sides of the hardened bolt side spines!!!!  Do not try to peen the bolt head metal into the key metal, nor strike the bolts heads directly.

Ditto, since there is no way of really telling why the key bolts failed in the first place.
Hence could be that they where over torqued to begin with, or even too much pressure applied at key staking to causes them to fail instead.

Bluntly, you have the softer key metal that will peen no problems to hold the torqued bolts in place, but the bolts are heat treated, and do not want to be over torqued/stressed isntead. To take it one step farther since the bolts are hardened, once they have been torqued to spec, they really are a one-time use since re-torquing them over again may lead to them failing quickly intead.

So the rest of the B/C may be fine, and it will be like throwing the baby out with the bath water by replacing the entire B/C, when its just the bolts that need to be replaced from a improper install instead.  Hence if you have a defective tire on your car, you replace the defective tire; not the entire car.