IMHO, if you had a major issue like a dropped valve seat, you would already know you had a massive problem. Trust me, been there.
The fact that the other plug is intact suggests no dropped seat, otherwise it would be mashed to heck.
Bad gas at one point starting detonation or pre-ignition combined with lack of maintenance (or vice-versa) can cause this.
Question for others on the coil pack... is there only a single secondary high voltage winging as in all other dual plug, single coil applications that I have ever worked on? If so, the plugs will use each other for a "ground" to complete a circuit. One bad firing plug would be unrelated to coil condition in that case (both would fire poorly).
: EDIT : I just checked a coil pack and see three primary wires and the two exposed secondary coil points do not have continuity.
Suggests to me that the coils indeed are separate for each plug (allowing much greater control for staggered timing to plugs - neat).
Therefore i've blown my own theory of one pack affecting both plugs out of the water.
Your coil is likely : EDIT : "potentially" fine, just the rubber boot abused on that side by the ever increasing gap it had to fire across and hot as heck.
There is a "spring" that sits within each rubber boot that connects the end of the spark plug with the coil, i've had these drop out, so keep an eye out.
This may also have been damaged by any "arcing" between the spring and plug.
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If it were my engine (with your description of how it was running) I'd replace all plugs, re-use the coil and see how it runs. Of course, look at all other maintenance items that have been left too long!!!
For what it's worth, I have previously replaced ALL coil packs based on questionable advise from "the internet" that made no difference at all, other than a lighter pocket. The coil packs are relatively simple and rugged and rarely an issue, much like an old school model T Ford coil pack. Any "smarts" are handled by ECU. I may be wrong, but perhaps a Chrysler tech could tell you how many genuinely "bad" coil packs they have replaced in their career.
I hope that my 2 cents helps a little.
As far as GOOD ADVICE goes, this is an awesome group that will chip in here and steer you right.
Good luck.
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