hi piorv2, just a thought, if you can't get satisfaction from the manufacturer and you're going to keep the set, try making or buying a rubber washer that can handle relatively high temps. when you tighten the screw, it should compress on the rubber washer, sealing out moisture.
if you can't find a suitable washer, but a high temp rubber pot holder and cut out a circle to fit the lid and handle properly.
in nomine patri, et fili, et spiritus sancti.
Meh nom eh noh...doot dooooo do do do.