I tried to get a rebuild kit from the dealership for my FJ60 box.. and was told not available. The FJ60 box is just like a IFS box, except it's a forward pointing pitman instead of backwards pointing.
So I headed over to my local bearing & seal shop in Emeryville, and got new seals for $15.
If it's the teflon seals leaking, your hosed. There is only one in the box that can leak to the outside - it's at the bottom of the box, in the sector shaft. There is a seal, a c-clip, a metal washer, an o-ring, and a teflon ring. The seal at this location goes down to get it out. And high pressure could possibly pop the seal out.
You might be able to pop that seal out, and replace it without tearing the box apart. Otherwise, it's a full teardown to replace that seal.
The other seal that is on the box, is in the input shaft. This seal can be replaced with out a full teardown; you simply pop the front nose off, and replace it. In my FJ60 box, there is no teflon rings in that location.
Both seals are available from a bearing/seal shop for total of about $15, plus any shipping (one seal was in stock in Reno, and the other was at their "other" SF Bay area location..)
There is two o-rings in the nose of the box - one seals a high pressure channel, the other seals the whole nose. These two o-rings is almost a full box teardown to replace.
The two other places on my box it can leak is the via the top adjuster nut - which uses a funky seal/washer, and the cap the adjuster is in, which is an o-ring.
Now, where is it leaking? If it's one the input shaft, it's just the seal. If it's down at the pitman arm, it's just a seal. If it's around the box guts, it's bad o-rings, and that's easy to fix too.
Or just go buy another used one that doesn't leak for about $100, and be done with it..