I thought about getting it calibrated, but I like having that extra bass range. It's useful for bleeps and acidish leads too, but overall its palette is pretty limited. There's a foam dust screen just under the front panel which turns into a horrible, horrible black goo over the years. Pull off all of the knobs and slider caps, open the case, and remove the top circuitboard. You'll see the foam overlay.
Rubber gloves are a good idea.
Mine has 6 broken keys, but then a cat pissed in it. I play it thru CV anyway. Amazingly, I've never noticed any tuning drift. Whereas my Moog Source takes half an hour to warm up before it'll stay in tune, this thing is very stable. I've heard that Radio Shack will still supply the schematics if you ask them.