Possible Water In Gas Tank Causing Power/Acceleration Issues?

Except that I wouldn't trust the old plug......or the coil or wire either.
An errant spark can create a carbon chain that just gets worse and worse over time.

I say replace the plug and coil, re-torque the gasket and clean things up good so that you can hopefully SEE any external oil leaks.

 

You mentioned no Check Engine code... did you check for pending codes?

Also, rather that throwing $$$ at the problem by guessing at replacement parts... Have you considered simply swapping the suspect coils/plugs with the good ones (i.e. swap coil #4 with coil #3 and a good plug with a bad one etc.). If the problem follows the part you can then buy a replacement with confidence you're on the right track.

 

Good job. You creatively managed to make progress in an efficient and cost effective manner.

I though you were using Torque with your Android... that's why I asked about the pending codes.

Having Techstream, you can get more codes (permanent / historic codes) that don't show on the free app.

Are you now seeing improved readings on the Torque screens... perhaps you can share the before and after results?

 

Something to consider:

If you are having those problems (leaking spark plug tube seals) I doubt they would magically get fixed by themselves (and would still be leaking). Since you did not find any oil in the #4 hole where you found the coil discoloration and you don't know the history of the car... it's more likely that the coil came from another car (and thus a separate and perhaps not related issue).

 

I'll just throw this out there, if there is enough oil in your combustion chamber to overwhelm the spark plug and coil, then you have some serious problems with that cylinder internally. I would think that you would be able to see burnt oil smoke from the exhaust.
It may be possible that the seal had failed shortly before you pulled that stubborn plug, but not enough oil had leaked into the well to show on the coil. The burnt oil residue in the well may have been the actual cause of the removal resistance of the plug.

 

I once had water in my intake manifold of the gen 3, causing some engine hesitation particularly in the mornings. This was part of a TSB issued by Toyota for a replacement intake manifold. Anyways, i used Heet water removal Additive and it seems to fix the problem after a 50 miles drive.