Just wanted to note my experiences with a seized plug....the evil rear trailing plug, which I think was already cracked. Looked basically like the plug in this thread, except with a little less metal: https://www.rx8club.com/series-i-trouble-shooting-95/stripped-spark-plug-any-suggestions-184300/

Took a lot of bracing and 4 foot breaker bar to get out... Scared the crap out of me actually.

After looking into what it takes to drop the engine....figured trying to fix the threads wouldn't hurt. I used this from Autozone.

Covered the tap in sticky-as-crap (red) grease to trap the chips (hopefully). In 1/2 turn. Clean it. Grease it. 1/2 turn deeper. Repeat 15 times or so...really hoping I trapped all the metal.

Then vised up the tap and ground it down to a flat end since the hole bottoms out. Repeat grease tapping some more...

Moment of truth: the block held the new plug well, without binding. As best I could count, it took the same number of turns to get to equal torque as the other new trailing plug.... So I think there is a good chance it's in there alright.

Won't really know until it's all back together, and I see what happens when it runs. But hopefully... We shall see. Now...to continue with replacing everything else on the car for it's 60K. (A 2004 still running great, even with original coils and everything! Even the fuel sock was still almost clean.)