i have two gibson cases from the 70's with the same problem, a fusty smell, which the guitar picks up if you leave it in the case. the irritating thing is, the first one was fine until i left it with a "tech" and he kept it in his damp shed! so i too would be vert interested to hear any solutions to this. i have tried both febreze and baking soda, with no improvement. and airing seems to have little effect. i would leave one outdoors to air, which might work better, but the fusty smell is better than cat piss! :)