You are correct on the prior loosening problem. I totally disassembled, brushed & cleaned threads and holes with acetone and locktite every bolt before reassemble and test operations.

Bolts are 10-24's Mount is .135" thick so lost 3.25 threads (22% of grip length) It will be interesting to see any difference tightness of broken stubs to remaining bolts.

Are all allen head bolts created equal? No but how are they marked for grade/strength? A reference site would be quite helpful.

Initially, my thought was that probably the self-tapping bolts would be of a higher quality/strengh. You cost / lowest bidder has its merits as well.