If you are using a new seal that all of the vendors sell , be ready for a fight . Lube both the body and the seal . I usually get the bottom and sides set and then go about working the top in with a tool while pressing and gently beating on the outside . Make sure that the lip of the seal is up Against the pinch weld before pulling the strong .
      The guys at G/W say they break a few windshields trying to install these seals .
         Good luck and keep the name of a pro near by.

                                                        Stacy

     Boy Scout " Wood Badge " trained.