I always install the seals after the cases are assembled. I fabricated a “tool” just for the job. Basically it’s a hunk of tubing that fits over the crank, and a large washer that lays on the seal. On the primary side use a bolt that threads into the crank end to draw the seal in, and on the stator side, use the nut on the crank to pull it in. Works perfect, pulls them in nice and straight every time.