I would look at it this way. If you are concerned about opening it might ruin it or its value, what happens if you don't open it? Maybe you clean it up and sell it, or sell it as is. In that case, whoever buys it might open it and find something valuable inside. If you plan on keeping it, and just sitting it on a shelf, the suspense will kill you. I would just go ahead and open it as carefully as you could, trying to preserve it if possible. But I'd open it for sure. I would not let someone else have the possible riches inside, nor would I just let it sit there always wondering. But that's just me..... ha