It was quite easy to change to the PSS-seal. The problem was linked to the "great" space around the shaft.
I hade to make a bigger hole in the wall between the engine compartment and the space behind (where I have my batteries). I did that for hand with a small tiger saw. Before that I had released the shaft from the engine and pushed it backward, to get more working space. (Check the end of the shaft to make sure there are no sharp edges - they can destroy the new seal.) With a bigger hole it was "just" to get down to it and mount the new seal, according to the instructions. I fixed the end of the venting in the starboard locker, to make sure it's over the water surface.
Take a look at the pictures and good luck!