JFP, sounds like the 5speed half shafts physically won't fit (shorter or longer?), so the idea of the last owner using a set of used 5speed half shafts on a 6speed trans isn't the cause of the leaks on both sides of the trans at the output shafts.
Okay new seals for the output shafts, pulling those suckers out, new seals, and pound them back in it will be!
Brian