The front output shaft yoke seal is very, very expensive. The seal is made with two metal sleeves, an inner and outer. They must be pressed in place at the same time. The inner sleeve presses on the shaft and outer sleeve into the bore in the housing. This installer makes it a snap. At fifty bucks a piece for the seals, you only want to do it once.
Call Omega Machine & Tool, Inc. for more information. Or you can bug your tranmission parts supplier to stock a couple.