Rusted spark plug well/mating surface - is this a concern?

[wild.coast]

While changing the spark plugs on a new to me 2014 50hp Yamaha outboard I noticed that 3 of the 4 wells have a fair bit of corrosion in them. This corrosion isn't just in the 'outer' surface of the well but extends to the machined mating surface against which the spark plug metal washer would seat.

Is this a concern?

I'm guessing the uneven corroded surface might mean that the spark plug doesn't seal/seat well causing some leakage and reducing the engine compression?

Any advice on how to clean? I don't want to go to down with a drill-mounted wire brush seeing as brush metal bristles might end up in the combustion chamber. I tried to scrape it a bit with a pick but also worried I might mar up the surface and do further damage
I'm guessing this is a common issue, any thoughts or advice?

Some pics for reference:
Two of the corroded wells:

Upper spark plug well is nice and clean (how it should look like for reference):

 

[Lou C]

Looks like the rust is from the body of the spark plug maybe they weren’t marine grade. I would replace the plugs then spray the area with a corrosion dissolver like Kroil then spray with carb cleaner & compressed air. Less risk that way.

 

[99yam40]

big question is
why is saltwater getting onto the plugs while in the motor while running

 

[wild.coast]

Looks like the rust is from the body of the spark plug maybe they weren’t marine grade.

Yep. I figured it was either that or these were the original spark plugs that the engine came with in 2014... usually spark plugs are nickle plated, which serves as a sacrificial coating to protect the base metal from corrosion. But even if the spark plugs were high quality nickle plated, the plating can only last so long until it breaks down (no more nickle left to react) and the steel starts rusting. One of the reasons plugs need to be replaced every few years regardless of engine hours. Definitely neglected either way

Corrosion dissolver is a good idea. I might try that and then use a dremel on low setting with a scotch brite or similar tip -> safer than metal bristles I'd imagine.

I'd imagine the ideal way would be to pull the top end of the block so it can actually be rotary cleaned without fear of debris ending up in the combustion chamber. Maybe even have the corroded surface brough back to perfect level by a machine shop.

 

[FishMan001]

You can clean it out with an old small screwdriver and a dremel/wire brush. First, get a long bolt (M14x1.25) and screw it into the plug hole about 5 or 6 turns, then just clean up the area. You can get rid of the remaining bits with a squirt of WD40 etc.
Unscrew the bolt, put a little bit of waterproof grease on the seating and put in your new plugs.
You don't need to worry too much about the seating not being perfectly flat; by the time you have pinched up the plugs, the gasket and the threads will have sealed in all but the most imperceptable bit of compression.

 

[wild.coast]

@FishMan001 great advice, that's super helpful!

Ended up doing something very similar to what you suggested, but used a paper towel and some thin wire to plug the hole and prevent debris from getting in.

Managed to get the mating surface way cleaner/flatter. A bit of pitting but no more rust caked on!