Years ago we were cleaning out my aunts house and we came upon her featherweight sewing machine with case. The case had that same musty odor you mentioned. My mother and I tried everything we could think of to get rid of that odor to no avail. Sunshine, newspaper, charcoal, you name it. We finally got rid of the machine. I still have our mother's machine. It has no odor and I presume it's because the machine was in almost constant use by my mother, two sisters and myself! I wish I had a happier ending to tell you about that sewing machine case. Sorry! Put the machine out and enjoy it and store the case far, far away.