Do you continuously operate the air conditioning system?
Is the air conditioning functional?
Is there any moisture present on the front carpets or in the wheel well of the boot?
Does the automobile only do short trips, so preventing the air conditioning system from adequately removing moisture?
Apply gummi care to all the door and trunk seals.
Inspect all the drainage openings on the front windscreen.
Has the pollen filter been changed within the last several years?
Verify that there is no water flowing down the windscreen scuttle and into the area where the pollen filter connects with the bulkhead in the engine bay.