The extension can be used when here is not a correct seal between the housing & the doubler input shaft because the input shaft may not be quite long enough. You may no have this problem. The extension housing comes with a seal. The seal is Timken 710058

http://www.jeep4x4center.com/teraflex-automatic-seal-extension-tf-2904400.html

97 Exceed, 3.5l SOHC auto, 4.90 gears, ARB front locker,rear Harrop E-Locker, Magnum winch, dual transfer cases also 2008 NS swb Pajero, front bar & winch