To check the door & boot seals, first give the rubber seals a visual check for any damage.
If all looks well, lightly smear the contact area of the rubber seal with grease. Close the door and open again � check that the rubber seal has made contact with the doorframe over the entire seals� length, from the line deposit of grease on doorframe.
If there is an area showing no contact, examine the seal for wear/compression. You may need to replace it.
Bear in mind that water/moisture may be getting in via other means.
Don�t forget to remove the grease from the doorframe and seal.