Genuine seals are available from milners for less than half toyota price.
When putting new seals in they only go in about 5mm, be careful not to damage them by pushing in with screwdriver.
Mine both went within a few days of each other, i guess they perish over time.
I worked out that mine were perished quite high up on the seal, they would leak after a drive, and once wiped and oil settled wouldnt leak again as oil wasnt being spun up.
As a temp measure I would jack truck up at end of day and then fill up, overfilling the diff so it was ok for next day (this was in Portugal so no garage).