And here is where the problem lies.
Throw the 12 point socket's in the garbage.
This is what rounded the heads of the bolts to start with.
Especially with an impact driver or gun.
Hammer a 6 point socket on the bolts, then wack them with the impact
driver.
12 point sockets are not to be used with any impact tool.

Propane won't get the flex plate hub hot enough to loosen the bolts
either.

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 I might try hitting it with a propane torch and hammering in a bigger
12-pt, add some curses if the kids are out of earshot....