not sure if the W/S manual attached gives more info. Depends on what you call the seal. The metal channel held by brackets 7 and retainer 6 has a rubber insert, if that is what you are referring to it can be replaced by removing the channel. Have done it not so long ago.
However if you mean the seal between the screen and the base unit (for want of a better description, on the inside of the screen) then I imagine the screen must come out.