Pulled a stupid move. Now I have to pay for it.

[moparedtn]

Left handed drill bit will work.

I blew a bolt head off on the front driver side valve cover bolt one time. Tightening it with an extension and I made contact with the + battery and it melted the head right off lol.

I snicker because I been there....didn't harm anything, but it was a startling show for a moment.
Learned to use the "baby" ratchet from then on for that task.

 

[MoparRobTX]

I had a similar debacle, but it was from prior owner. I had a leak and there was a ton of RTV on the edge of the valve cover. I went to unscrew the bolt and whoever did it had RTVed the bolt onto the valve cover because it was snapped off in the head. Of course it was the rear of the valve cover. Easy out wouldn't work but finally was able to drill it out with small bit and got it out and re-tapped the threads.

 

[niteshift70]

Are you using factory stamped valve covers? Any stamped covers, even aftermarket ones, will dent at the bolt holes after a couple gasket replacements. Folks can't help but overtighten them installing the covers or trying to stop leaks. Cork crushes under the bolt and gets thin or pinched in two. I like the stiff Felpro rubber gaskets or RTV by itself. Cork ain't good for anything but fishing bobbers.
Get a ruler or straight edge and lay it across the gasket side of the valve covers over each hole one at a time. It should lay flush the entire length of the ruler. If the surface at the hole is elevate above the gasket flange surface, the bolts have been overtightened and it will be very difficult to stop them from leaking, even with the stiffeners. Find something you can use for an anvil, like the corner of a table or workbench, or a deep well socket. Hold the valve cover bolt side down against the anvil and gently flatten the raised section with a small hammer until your straight edge lays flush. Do this with all the holes that are bent. Reassemble with your preferred gasket and use the stiffeners (they help prevent overtightening and spread the clamping load). Run the bolts down until the cover just flattens the gasket to the head, then working from the center out, give them each 1/4 to 1/2 turn. That should be enough to seal them without crushing the gasket or denting the covers.