If your filter is leaking between the motor and case, there are a few things to check.
1. Any dry spots or cracks on the motor gasket? The gasket will need to be removed from the motor to check. A silicone lubricant can be applied to dry spots. A new gasket will be needed if any cracks are found.
2. Any debris on the gasket or in the groove on the motor head? The gasket will need to be removed from the motor to check. The entire gasket should be cleaned with water, as well as the groove on the motor head. Using Q-tips or something similar to get into the groove is best. Applying a silicone lubricant to the entire gasket before reinstalling will help protect and extend the life of the gasket.
3. Any debris on the top edge of the canister case? The top of the canister should be wiped down with a damp cloth during each maintenance. This will help to ensure no debris is there, or can be transferred to the gasket.