Rusty Spark Plug, no oil residue

My old 2008 Prius has been experiencing misfires and I wanted to ask for help.

Specifically it has been misfiring on Cylinder 4 and I just changed the plugs and there was rust on the outside of that spark plug but no signs whatsoever of oil on the outside of the plug or in that spark plug well.

I wanted to know if there is a chance that a gasket or seal leak could cause this? --rust but no oil

There is also the chance that this is just rain water getting in from outside the engine as the car was driven much less frequently than normal when its catalytic converter was stolen and then replaced within the last year. I live in a very rainy climate and have to frequently clear out leaf debris from the windshield wiper motor cover.

I have switched coils between cylinders 3&4 and am expecting to replace a coil in the belief that the moisture may have damaged a coil. If the misfire comes back on 3, I will change a coil. I will also caulk the central joint on the wiper motor cover as this joint is very close to being right above cylinder 4.

I do have photos of the plugs and plug well. They are very clean with no oil. The well where the water got in has rust from the rusty plug ad the alloy is not as shiny as the other plug wells.

The coolant level has been steady and the coolant color looks good.

The other problems that the car has are that the gas tank bladder is reluctant to fill and the car misfires if the the tank/bladder is overfilled/topped-off, the car also does burn a bit of oil at 187K miles.

 

Thank you for the reply and suggestions. I will go ahead and replace the coils. I will look through this forum for suggestions on the most legit places to buy parts. I'm fairly sure that the plugs that I bought through Amazon were legit but I'll be more careful with purchases of more expensive parts.