1999 Honda Accord Plug Wire

I have a 1999 Accord v-6, and while driving on vacation, it decided to act up - very rough idling. This has happened a couple times prior, but then it occurred when initially starting the engine, not as I was driving down the interstate, and it lasted about 1 minute as I turned the key off, then on and it was idling fine. This time, it did not go away. Made it to the beach, popped the hood and saw one of the wire boots was not on. Played around with pushing it back on, but it always seemed to come off. Replaced #6 wire, as well as cleaning the area with brake cleaner. There was some fluid in the plug chamber, but not excessive. (The counter help at Napa gave me a inquisitive look when I said I was replacing the one wire right then and there. I guess he didn't think I (a female) was capable of doing so.
I made it home and the car is scheduled with the mechanic to replace the remainder of plug wires as well as check why there was oil around the plug. One note, the plug was 1/4 turn loose and it was tightened when the single plug wire was replaced.

What could have caused the spark plug to loosen in the first place? The plugs and wires were replaced in 2008 --- I didn't know they would need replaced so soon.

Also, I've noticed the fan doesn't kick on like it used to. In the past, it seemed every time I pulled in the garage and turned off the ignition, the fan would run. I can't remember when it came on last - or at least I'm not noticing it. The temperature gauge sits mid in the temp gage, at least for the past couple days when I've been monitoring it. Is this normal? If not, what might be the issue/concern?