I have used silicone for years. Glue it and you may never be able to repair it again. A good clean contact surface area, small amount of silicone and work the new gasket down into the groove to remove air. I usually put a small amount of silicone lube on the gasket top and let the diverter squash it all down and hold. Have the customer leave it off for several hours, even a day.
The culprit here though, is moving that dial valve without first turning off the pump and letting the water actually come to a stop. The water is traveling very fast inside the dial valve and if the diverter gets lifted while the water is flowing, it will just peel the gasket up.