Very little info on this, I'm guessing this is well within my 'why pay someone else to do this' zone. Have the seal and seen the illustrations does the output shaft have to come out to do the seal? This will be an in vehicle job- 1990 4Runner. Also what mostly the causes for these leaks- plain wear or a wonky shaft- I bought the unit used and don't know the history although other than the odd snowbank I haven't impacted the box on rock. Thanks