Contact you local dealer about the seals. I had the same problem that you had with my 97. I took my truck to a local mech. and they "fixed" it, and a few days later the problem happened again. I took it back to them and they "fixed" it (again). I drove it for a couple of days and guess what?? it happened again. So then I took it to the Toyota dealership and told them what had happened. They told me that they received a revised update from Toyota on how to make the proper repair to the rear axle seal (updated information that the local shop would not be aware of.)
After the dealer worked on my truck there have been no problems.