I have the Lionel Penn U Boat from several years ago and the same drop out happened. It was the vol pot also. Turned it low to high repetedly and blew air across it and has never dropped out again. The vol pot must be installed in order for sounds to work so it was worth the try. Think about an old radio that scratches when the volume was turned up or down. Once moved rapidly up and down the scratch sound went away. That was my reasoning.
Rod Miller