Make sure the problem isn’t with the height adjust screws or springs. Make sure the components are firmly tightened and chatter free. Wax potting would probably be my first choice and that it’s properly done. Silicone can be put inside the top of a metal cover such as on Fender Telecaster Rhythm pickups. If needed the silicone can be removed at a later date. The wax potting will leave a wax coating on the bobbin and can cause a small problem in rewinding the pickup and you need to glue the bobbin if it becomes loose or broken. It’s hard to glue parts with wax on them.