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It may already be gone, and loosening it now is pointless.
If the head is damaged, you'll find it out when you use full throttle and the plug blows right off the engine.
I floored the 2003 RX300 today, and with 174,000 miles it screamed like a brand new car. Felt like the day I drove off the lot when I leased my new CT200h. Mechanically it enjoyed being floored. I stopped after a few lights. The transmission was shifting smooth under the higher pressure. I went home let a cool for about 30 and left again. This time I was just driving miss daisy, and enjoying the slow drive. Seemed going uphill the transmission makes a small jolt occasionally when down shifting, or up shifting under a slow acceleration. Really scares me hope the transmission holds for another 100k. Im guessing the spark plugs are A-OK after something like that.
** Raced and tied an earlier 2000 BMW 328 leaving the owner stunned.