dmorgan, measure 1) the thread projection of the two bolts past the end of their respective spacer sleeves, and 2) the depth of the blind holes in the head. Those dimensions will determine which length Helicoil to install. Now you know why oil accumulated in the spark plug holes. It's likely a tech stripped the female threads in the head using an air tool, and did not want to take the time to repair his mistake.

The Loctite Threadlocker keeps bolts from loosening due to vibration. It does not repair stripped threads.

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Fred Hoelzle