Switching base on Knoll Life chair?  

I have a Knoll Life with a plastic base and am attempting to switch to a metal one. Knoll informs me that the plastic base is "press fit"--that is, it's just tightly fitted to the metal cylinder--and that I should be able to pull it off by hand. Failing that, they suggest a rubber mallet. Well, I'm a pretty big guy, but those tips are not working. I've also tried WD-40 and a Teflon lubricant (separately), but perhaps could be more generous with the application of either/both.

Below is picture showing the base/cylinder combo. (Not from my chair, obviously.)

Thoughts? Thanks in advance.