Earl I have to ask if that is due missing maintenance. When last was the rear end stripped and lubed?
June of 2015 (13,600 miles ago) is when I installed that tire and did the splines lube with Honda's Moly Paste. The seal was in good condition, but it clearly didn't mate well with the pinion cup and tore. I probably boogered up the seal and failed to notice it while getting the driveshaft to couple to the Ujoint.
Surely you've done that dance called the "Daniel Meyer driveshaft wiggle". Well, it's best done without the final drive anywhere nearby, just the driveshaft.
"Earl's Alternate Method" made that coupling happen with the final drive fully on the wheel, its studs started to the swingarm with no nuts, boot partially off and right hand helping align the ujoint. THEN, I coupled the ujoint back to the engine while seating the final drive to the swingarm by rolling the tire forward with my left hand.
I don't recommend that method. I've since then attended IZ16 and seen Daniel wiggle for the class.
All kidding aside, that seal, 91261-ME9-005 is $7.50 well-spent, as previously mentioned.
Edit: As for the Ujoint boot, it was stiff but intact at the time of tire installation. I ordered the new boot based on the difficulty of reinstalling that old stiff one. I haven't pulled the boot yet, but it may be holy, which would account for the water in the swingarm that migrated past the torn oil seal at the pinion cup.
