Was going to clean my spark plugs while ago and when I went to take off the thumb nut the whole plug turned. I had all those plugs out a couple weeks ago. I can't believe I didn't tighten them. I've driven it plenty since, washed it Saturday and didn't open the hood til Sunday and 3 were holding water so they were sealing ok. No big deal I guess but I don't know how they got loose. Maybe I didn't tighten them.
Must have been left loose. I would change the oil in case the 1 let water in the engine. That's just me. Tim