I just bought my first house and one of my first obstacles is the radiators. I managed to remove them all so that I could strip them and paint them, however I found one valve missing the knob. Then I found out why after I purchased a cheap replacement knob and broke it. It turns out the valve is stuck. It will not open or close any further than its current state. I put just about all I had into trying to make it budge to no avail.

Then I decided I would just replace the entire valve set up, but that is stuck too. HELP.

Details: One pipe steam radiator system, likely original from 1925