Hi gn. Please post a couple of pix and maybe we can get a better idea of the severity. It is possible to use the same strategy, and the more likely avenue is going to be a light sanding. If you are talking about painted interiors, you could test out some 3-0 or 4-0 steel wool in a small area to see if it comes up. And once it is out, go back with a bleach solution, lightly, and let it dry completely before closing the drum up again. You did not mention the brand. This will have some impact on how aggressive to go.

the interiors seems to be all naturals.. maybe that's why this occured, never seen mildew on painted interiors..

I dont know the brand, think its an old japanese pearl.

If that is the case, I would sand them with 100, then 220, then hit them with a light coat of lacquer, or maybe some light poly. Like the Minwax, because it is very light and thin, almost watery going on. It will seal the surface, without completely encasing it in a layer of plastic. If you have a can of lacquer or other natural type surface protector, use it over the poly as it will have a warmer sound, but you should only use a very light coat, no matter which you use. Being they are the thicker lauan shells, it won't hurt them, or the value to seal them up, and might make them sound better. Before you coat them,

I would play them first to see if the sound is good after you sand. If it is, leave them alone, unless you think the shells really need a coating. I did my old no-names after the veneer went in, but that was pure choice, and they sound awesome, with the exception of a little ringing in my mt, which I am working out, slowly but surely.