Misfire and valve cover gasket fix

I have a 06 with 245k miles. I did the most extensive engine repair ever completed on this car over the weekend and thought I would share my experience.

The engine started running rough last week, and got a lot worse quickly. Was getting trouble codes P0300, P301, P303, and P304. All misfire codes (300 is random misfire, 30x codes correspond to their respective cylinder numbers. Started with the simple stuff, cleaned the MAF and throttle body (stab in the dark). Then pulled the coils and plugs. #1 looked fine, no issues. #2 had a small amount of oil on the plug, coil end only. Coil was clean, and firing side of the plug looked normal for a plug that's been in 50k miles. #3 plug had even more oil on the coil side, none on the firing side again. Electrode was worn pretty good on this one (I use NGK laser iridium every 100k miles).

#4 was where things got really messy. Heavily oil soaked coil, and oil dripping from the upper portion of the plug. Firing side looked good though, little wear. Best I could tell from the condition, I had a valve cover gasket leak at the spark plug well connections.

Repair went fairly smooth overall. Removed the air filter box, unbolted and moved the engine wiring harnesses, removed the coils, removed wiper blades, linkages, motor, and tray. I had to unbolt the brake fluid reservoir and move it out of the way, but did not have to disconnect any hoses thankfully. All the valve cover bolts/nuts were 10mm, about 10 of them I think.

I have never done a valve cover gasket before, I was surprised to find it VERY fragile. Parts of it fractured like glass when I went to remove it. I was careful to collect any broken pieces. New one went on fine, after cleaning the surfaces with carb cleaner and a rag. Used black RTV sealant on the timing cover joint/seams and let it cure. Also used the new center bolt rubber gaskets that came with the gasket kit.

Overall, probably took about 3 to 4 hours or so, but I was going slow and taking my time. In addition to the gasket, also replaced the PCV valve, all 4 spark plugs, and the #4 coil that was probably the source of the misfire in the first place. Engine runs smoother than ever now. Verified that there are no leaks. I pulled all 4 coils out after the test run-in and verified no oil in the spark plug wells also.

A couple of questions for any mechanics on here, do you have a good suggestion for how to get the residual oil cleaned out of the spark plug well? I mopped it up the best I could, but there was still some varnish residue in there that wouldn't come out too well. Also, when I went to pull the plugs out, #4 plug was very loose in the engine. Really only finger tight. Why would that be? When I replaced them at 200k, I torqued everything per spec, so was really surprised to find it loose. Could it have simply rattled loose from the vibrations of the misfire??