Success!
I spoke with an A&P buddy of mine who suggested an LPS Product, PreSolve which is actually a Penetrating Cleaner/Degreaser. Well the local Industrial supply store didn't carry that particular LPS product so I looked at what else they had in the penetrating oil department. I found Aero Kroil which is made by Kano Labs. They start their claims with a money back guarantee followed by stating their product is,
"an industry proven penetrating oil that has no equal. Quickly loosens
rusted nuts and bolts - frees frozen shafts, pulleys, etc. Penetrates to 1
millionth inch spaces, dissolves rust, lubricates, cleans and prevents rust.
Displaces moisture. The oil that creeps."
Figured with a claim like that, maybe it'll help this 33 year old O-320. So, I sprayed down the seam on the case, all the bolt holes a few times over a couple hours. One tap from the dead blow and there it split.
Needless to say, I was impressed.
I spoke with my Dad about this product. He's a NDT inspector for Lockheed Martin. He said it sounds similar to the stuff they use for doing penetrant inspections, less the ingredient that glows of course.
If you ever have a stubborn assembly, bolt, etc. I suggest giving this stuff a try.
www.kanolabs.com