White eroded plugs, stuck plug, and part question
 

Just bought a '11 Crown Vic w/ 270k miles a couple months ago and finally got around to replacing the plugs today. They all looked like this..


https://cimg1.ibsrv.net/gimg/www.for...793d8882d4.jpg


https://cimg4.ibsrv.net/gimg/www.for...f472febab0.jpg

All with heavy white deposits as well as both top and bottom electrodes eroded. Gap on these should be 41-47 and they were measuring about 80. So first question is what do the white deposits and eroded electrodes indicate?

Everything was going well until I get to the last plug in cyl 4, all the way back on the left. Thing was/is in crazy tight. After cranking back and forth for a while the best I could get out of it was 1/8 turn. It moves fairly easily within that limit but comes to a dead stop at the ends of the turn. What could have caused something like this? I think the mechanics taking care of it before me were hacks. Car started out as a police vehicle then was a cab before I got it.

My only idea is to heat the engine up and see if it'll twist out. Although I'd have to be careful as I'm sure hot threads would strip easily. Not really sure if that'd be a good idea.

Any advice on how to proceed here?

And last I broke a tiny clip at the end of the tube in the bottom center of this pic and have to replace it now...

https://cimg1.ibsrv.net/gimg/www.for...046303728e.jpg


I think it's part of the evap system but not sure. Anybody know what it's called, part number, or how I would search for it on ebay?