You can open and clean the crossfader, if compressed air wouldn't clean enough. Mine was is also nearly 20 years old and spend a few years in a club. after cleaning the rails it went perfectly.
See my rotary mod, maybe you don't need to buy a urei. It's not difficult to build
For your output:
Have you tried to turn the output and meter sensitivity on the back side of your mixer down? I have the output full down and the sensitivity at about 0.775V I think.