Yesterday was the first time I had the PTO off to see the bad seal first hand. The seal was very loose in its bore, you could rotate it with your finger!
As loose as it was, it had to be leaking lots of oil from the metal to metal mating surface, rather than from the rubber seal to shaft surface. I ordered the incorrect front seal online before disassembly, and read down the crankcase list until I found front seal. You are correct, if I had studied the exploded diagram more carefully instead of scrolling down the list, I should have seen that the rear seal was located behind the PTO. Live and learn. I'll always remember now that a Magnum installed in a Cub is backwards. I will try and reseal the electric clutch and get some more use out of it.
It will be nice to mow with a quality machine again soon after using a hand-me-down Wal-mart mower so far this year.