If you can avoid pulling everything out, do so. Track your ground problem. What is the nature of the buzzing? If you take your hands off the instrument, does it buzz. Does it stop when you touch the bridge? The choke button? The pickup? Are those things sharing a common ground connection?
The Gibson repair people probably did not want to deal with the HORROR of pulling the wiring out of these things. I have done it several times, and trust me, it sucks. Plus they have very often been monkeyed with. Is the choke still hooked up? That gets yanked a lot. Sometimes it is easy to fish the wiring out to re-hook it up, and sometimes the choke is clipped off, or dug out. And any messing around runs the risk of breaking the ground wire from the bridge stud, as it was/is typically bare utility wire and easily snapped off. If that happened, you have to pull the treble side bridge stud. Oy!
There are basic wiring diagrams that I can post, but if you are going to wade into the very fire of hell by re-doing it all, then I strongly suggest you consider doing sleeper mods while you can. As long as you add no holes, or lose the parts, you don't really do any harm, and it makes the bass more fun for sound. The EB2 has lots of room to play with.