My S4s also had leaky seals but I had scored the case when removing a seal so I bought a used replacement case and adjustable nut after having had the score filled in with weld then honed.
Replaced axle bearings, axle seals, o-rings, rollpins, MT-90 and also bought seal tool. Used HondaBond on splines and 180 degree offsetted rollpins. After filling trans and it sitting all night I noticed a puddle from a right side leak and I followed manual precisely. The problem was that with new fluid it hard to distinguish leak being from axle or threads. Think the axle is the likely culprit.
Face of axle where it touches differential has no burrs.
I don't think my adjustment nut was from the case I got but that should not of mattered.
I did install seals dry and maybe I should of coated outside with HondaBond. I will next time even though left side is not leaking at this time.
Since I replaced bearing I did the spring scale check on differential backlash. My nut is roughly eight full turns when I remove it and the new leak discovered. I wonder if that is normal amount.
Due to broken hip in January (now walking on it without assistance) have not been able to get back to it. Hoping to learn from these 2 threads.
Rich F
P.S. This entry repeated on other thread of same subject.