We leave our RV parked in Arizona and use it only during the winter months. Each time when we arrive for the season, the rubber around the toilet valve (ball valve) fails to seal for about a month allowing the water to leak out of the bowl. After about a month, it finally seals for the rest of the season. I'm assuming it just drys out. I've tried spraying it with silicone to no avail. Any suggestions on how to treat it so it will seal immediately?