A friend wants to fix a Ruger AR ,
Same as You described?
Push the stupid 'bullet button' in as far as possible.
Grasp the bar on the opposite side of the receiver.
A skinny rod connects the 2 pieces.
Sever it with a cut off wheel, (small), on a dremel or air tool.
Simply replace the offending pieces with stock MIL-SPEC parts.
IF it is an early model, there are Youtube videos showing how to screw the bullet button out using a spent .22 shell slightly modified. I've found they got wise to that and started bonding the threads.