I've got a Gibson Ripper that was my main bass for several years back in the 90s but it's spent most of its time in the case in recent years. A while back I pulled it out and was surprised to discover that the strings (regular old GHS Boomers) had become corroded. Now, at that point it had been sitting for a long time, so I didn't think much about it. I put new strings on it, gave it a set-up and played it a bit, but then it went back into the case, where it remained for several months. I just pulled it out the other day, and lo and behold, the strings are corroding again. But this time I noticed, the corrosion is only over the pickguard---they're not corroded over the fretboard, or on the headstock. These were new strings, and did not have a lot of use. If this was due to sweat or skin oils or something, I would expect them to be corroded where I fret them, and probably close to the bridge where I would do palm muting, but not over the whole length of the string where they are over the pickguard. Looking closely, there seemed to be some sort of oily condensation on the pickguard---definitely not just water. It would wipe off with a cotton cloth but not easily. The case in question is a Star flight case, not the standard Gibson HSC, for whatever that might be worth. Has anyone else observed anything like this? Or, is it known that old Gibson pickguard plastic gives off some organic chemical that corrodes nickel strings? The case was not damp, and the bass was not "rode hard and put away wet". None of the obvious causes would appear to apply. Any insight would be appreciated!