This was a very helpful thread and thanks to those who have contributed. I attempted this repair on my truck today, but I'm afraid I stripped the threads and now the old plug is stuck. I went very slow, loosening and tightening, spraying and waiting each quarter turn or so for about 45 minutes. As it started to loosen, it felt like I was at the top of the threads, but I could never pull the plug out. Now it won't loosen or tighten anymore, it just spins (almost) freely.
I knew there was some risk involved with this, so now I'll have to face the cost to repair the head or whatever else it might be... I just figured I'd share my experience with the group.
At this point, what is the safest way to move the truck out of my driveway? I don't dare turn the key on or start it of course.
Thanks again.