Cuda, The oil is a given. That PB Blaster is good stuff.
If he uses a good quality spark plug socket, or a good 6 point (not 12 point)
deep socket, I don't think he'll have rounding problems.

When you go to reinatall the plugs make usre you use marine plugs that have a stainless body. Using automotive plugs with that aren't stainless is the ussualt cuase of the problem you are having. Also DO NOT use a male easy out of any kind if the insert breaks out of it. If it is that stuck you will break the easy out and then you are screwed. They make female extractors that grip the hex portion of the plug if it becomes rounded that work very well. Heat and oil are the two best fixes though, heat from running the engine is not near enough either you need a torch to get real heat on it. Just be careful in the Bilge with a torch, make sure the hatch has been open for a while an have some soaking wet towels handy(wet towels don't make a disaster out fo the compartment like an extinguisher does.

IT IS OUT!!! YAAAHOOOO!

Thanks for all the advise.

Here is what I did. I used PB Blast to soak it down. I waited about an hour while I cleaned around the rest of the boat some. Then I used a 1/2 inch impact wrench set on 40psi to bang it around for about three minutes. The gun just fit between both manifolds and with a deep 6-pt socket fit in perfectly. After the three minutes I noticed a different tone in the impact wrench and stopped. I then took a ratchet to it and it BROKE FREE BABY! Awesome. This saved me mucho dinero and the sale of the boat.

Thanks again.

I love happy endings! :=). Thanks for posting the results. PB Blaster is your friend with a boat for sure.

I knew that would work. Glad to hear it's out.

Told you it would work

From my rock crawling days I had a CO2 Powertank (http://www.powertank.com/start.htm). It's portable, so was able to place in cockpit and dial the air pressure to where I needed it. I initially used a 3/8 impact gun, but it didn't have enough azz. Then I used my 1/2 gun starting at 25 psi and worked my way to higher pressures.

These tanks come in very handy for inflating trailer tires, suspension air bags, air lockers, changing tires, air grease guns (nice for triple axle trailers), etc...