Crap. I've been on this fill plug with an 18" pry bar a few times, and even with an impact. Both hot and cold. NOTHING.
Today I picked-up some stuff called Wurth Rost Off Ice. It is a freeze spray that can drop items to -40. I sprayed the plug, let it set for about 45 seconds. And then damned-near broke my face and leg because it broke-loose so easily. I braced to give it the shit and instead I can't tell you how amazingly easily it came out.
Sweet. Fresh fill of Redline D4 going in tomorrow. Along with a bit more anti-seize then I used last time.....