The critical question, Mark, is whether the melodica is playing properly. My experience with the Yamaha P-37D is that it does not have moisture problems, although the venting seems oddly designed. If notes are playing cleanly, as they typically do on this model, I wouldn’t worry about how blowing it out sounds or feels. On Yamahas, a note may occasionally choke, but I don’t think it has anything to do with the moisture venting. Moisture is vented into the inside of the enclosure, but it doesn’t seem to create any problems. This moisture eventually drains out or evaporates.