My knob has gone stiff

[mr.e]

ya I would pull the plastic knob off and spray a bit on the metal part

[waketek]

I hope you have not used WD40 yet... Never spray WD40 on an electronic device. This is what you want to use and it works great!
http://www.deoxit.com/

[Onkel Dunkel]

Somehow i knew this was going to get nasty with that topic name

To the intended topic:
Like waketek said; never ever use standard lubricant for electronic devices. You need some contact cleaner with lubricant. Doesn?t need to be a specific brand. Go to your local electronic shop and ask for some contact cleaner with lubricant and make sure you turn off power before using it and leave it for a while so that it can vapourise before turning power back on. If you are familiar with soldering you could of course change the potmeter. This might even be cheaper