Reply to uc-33e replacement potentiometers (knobs)

Hi,

My top left knobs on my uc-33e never stop to send midi value 52 & 53 as soon as i turn on the controller!!

Never had water in it! it started this morning and was working right yesterday evening ...

Since i don't have any kind of waranty on this i was believeing of buying a potentiometers (knobs) and replacing it myself... The only thing is i don't know what kind of knob i need are they special.... if someone could help me out with this i would be grateful

-t