If the seal head is similar to the 350x/200x, then you really don't need to replace the entire head. There are two seals that you can replace pretty easily and race tech should have them. There is also a big o-ring on the outside. On the 350x/200x, the top seal is in plain sight. The other seal is on the bottom underneath a washer held in by a snap ring. It isn't too hard to do, but definitely buying the entire seal head would eliminate you needing to deal with any of these seals.
- Frank
1984 200ES Big Red
1985 350X (x2)
1986 350X
1986 250SX
1984 Auto-X
1984 ATC70
1985 ATC70