Leaking Grohe 20.610 bathroom faucet

I have a leaking Grohe model 20.610 bathroom faucet. I have tried to remove the cartridge, but have been unsuccessful in unscrewing it out. The bolt does not move at all. Am I missing something?

Also, does anyone know if I just need a new O ring or do I need a new cartridge, and if so, what is the cartridge part number? The Grohe site does not have any info on the 20.610 (too old?).

grohe faucets

usually they just take a whole cartrige

I have tangled with a few and they are
very hard to get apart.... almost like the
cartrige is mechanically driven into the faucet...

thought I was gonna twist the faucet off the whirlpool tub

try some wd40 ,