The seals for the transfer case portion that contains the hydraulic fluid (clutch piston application fluid) is not serviceable. The transfer case also contains ATF for the clutch friction discs. The two different fluids should never mix together. If the hydraulic fluid fills the chamber that is intended for ATF only, it can start to leak due to an overfilled condition. This is usually indicated by a very low hydraulic fluid reservoir with no signs of a large leak.This condition requires the replacement of the transfer case. Hope this helps as your description is not very specific.