Not sure if I'm stating the obvious here, but PB Blaster is the best penetrating oil I've found - beats WD40 by a long shot. I've had luck with the propane (or MAPP) torch on the cup itself (watch out for the frame), followed by PB Blaster. I think the heat pulls the oil in further. Let sit, then tap with a hammer to (hopefully) break oxidation. Then crank on it. Good luck!