I have to constantly plug and unplug the patch cord into the instrument to get sound. Its almost like when you have to clear your throat alot in the morning. Either it doesn't get any sound at all, or its very scratchy and fuzzy and the volume control goes in and out alot....
Well, the output jack is what turns the preamp on. (The sleeve makes the connection of the battery to the pre. Pretty common arrangement on active basses.)
It's possible that the jack is boogered, but I'd suggest two easy things to try:
1. Make sure the plug on your cord is clean and shiny. An ordinary pencil eraser is a pretty good tool for cleaning it! (I ain't kidding ya! When I was a second engineer in a studio, I was always cleaning patch bay cords that way.)
2. After that, leave the amp turned off and just "exercise" the jack in the bass. In, out, in, out, in, out... um... like Freudian sublimation...
See if that helps, before you start changing parts.
Oh, yeah--you're sure the guitar cord is in good working condition, right?