You can try replacing the output seal with an OEM seal. If you do, be sure and put high oil resistant silicone (grey or super black) on the output shaft splines. Some times that can be the source of your leak even if the seal is fine.
If that doesn't work you can send your output shaft seal housing to a guy on MUD who goes by the forum name of MUDRAK. He machines out the housing and then installs double seals into it.
Randy Rosetta KDØKWX TLCA #19351 69 FJ40 "Meanie" & 1970 Boss 302 Mustang