Removing the knobby thing from the stopper - HELP!
 

Hello all:

I'm trying to replace a tub stopper. I did it on another tub by removing the little knob counter-clockwise, then unscrewing the big brass screw. The whole mechanism lifted right out. This other one is not budging. (I'm assuming it's the same design, since I see no screws under the stopper or on the shaft thingie.)

I lifted a pic from another thread to give you an idea of what I'm working with. I've used WD40, banged on it, tried to scrape under it with a razor. Any suggestions?

Thank you!