If the pots work, just get a little contact cleaner and spray inside the pots. This will eliminate any scratchiness or noise from the pots. DeoxIT D5 is a good contact cleaner that's readily available.
If you want to replace the pots you'll need to find out the rated resistance of the existing pot, usually stamped on the top or side of the pots. If the bass is passive (no batteries) the value/resistance of the pots will be 250k or 500k ohms. If the bass is active (requiring a 9 volt battery) the value/resistance will be much lower (25k, 50k, or 100k ohms).
It's a very simple bass to wire, especially if it's passive but if it aint broke...
http://www.seymourduncan.com/support...atic=std_pbass
