Hmmm, ...why were you removing the exh. ......??
Liquid wrench is pretty much worthless except for mama to use around the house. Use "PB Blaster" or the like. (Autozone)
I'm "8 for 8" now with easy-outs BUT, I've also broken my share. I would soak the remaining two with PB Blast. for a couple days.
I would remove head & prob. let a machine shop handle it. If the other two come loose then only one head has to come off.

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Check this out..! Some mach. shops have a piece of equipment that actually "explodes" the broke-off piece down in the hole.... somehow crystalizes it but no affect to main part.

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My man here has one but luckely I've not needed him "yet." [-o<