DEFINITION: A visible indication of an external fluid leak from the transfer case.

Review the Symptoms - Transfer Case and perform the necessary inspections.

Transfer case oil drain plug or oil fill plug leak

1. Inspect for the correct sealer and correct amount of sealer on the plugs. Refer to Adhesives, Fluids, Lubricants, and Sealers in Transfer Case - NVG 120-NR9 Unit Repair.
2. Correctly install the plugs. Refer to Transfer Case Fluid Replacement .

Vehicle speed sensor (VSS) leaking

1. Remove the VSS. Refer to Transfer Case Speed Sensor Replacement .
2. Inspect the VSS for the following conditions:

•	Cross threaded

•	Cut or damaged VSS O-ring

•	VSS over tightened causing deformation in the VSS

3. Replace the VSS O-ring if faulty.
4. Replace the VSS if faulty.

Rear output shaft seal leaking

1. Inspect for the following conditions:

•	Overfilled or improper transfer case fluid

•	Blocked vent pipe

•	Seal improperly installed, worn or damaged

•	Seal bore damaged or cracked

•	Extension bushing for excessive wear

•	Slip yoke seal surface for wear or pitting

2. Repair or replace the following components if found faulty:

•	Adjust or replace the transfer case fluid. Refer to Transfer Case Fluid Replacement .

•	Clean or properly route the vent pipe.

•	Replace the rear output shaft seal. Refer to Rear Output Shaft Seal Replacement .

•	Replace the rear output shaft rear bearing retainer assembly if the seal bore is damaged. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - NVG 120-NR9 Unit Repair.

•	Replace the extension bushing if worn. Refer to Rear Output Shaft Seal Replacement .

•	Replace the slip yoke if the surface could cause leakage. Refer to Rear Propeller Shaft Replacement .

Front output shaft seal leaking

1. Inspect for the following conditions:

•	Overfilled or improper transfer case fluid

•	Blocked vent pipe

•	Seal improperly installed, worn or damaged

•	Seal bore damaged or cracked

•	Missing or damaged front propeller shaft slinger

2. Repair or replace the following components if found faulty:

•	Adjust or replace the transfer case fluid. Refer to Transfer Case Fluid Replacement .

•	Clean or properly route the vent pipe.

•	Replace the front output shaft seal. Refer to Front Output Shaft Seal Replacement .

•	Replace the front half case if the seal bore is damaged. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - NVG 120-NR9 Unit Repair.

•	Replace the front propeller shaft and front output shaft seal. Refer to Front Propeller Shaft Replacement and Front Output Shaft Seal Replacement .

Transfer case to adapter leak

1. Inspect for the following conditions:

•	Loose mounting fasteners

•	Gasket or sealant faulty

•	The transfer case input shaft seal leaking

•	Cup seal in the input shaft leaking

2. Repair or replace the following components if found faulty:

•	Repair or replace the loose fasteners. Refer to Transfer Case Adapter Replacement .

•	Replace the transfer case adapter gasket. Refer to Transfer Case Adapter Replacement .

•	Replace the transfer case input shaft seal. Refer to Input Shaft Seal Replacement .

•	Inspect for the following conditions:

-	Seal improperly installed, worn or damaged

-	Seal bore damaged or cracked

-	Input shaft seal surface worn, grooved, or damaged

•	Replace the cup seal in the input shaft, if leaking. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - NVG 120-NR9 Unit Repair.

Leaking at the vent pipe

Rear output shaft rear bearing retainer assembly to rear case half seam leak

Disassemble and seal the seam leak. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - NVG 120-NR9 Unit Repair.

Case leaking

1. Inspect for the following conditions:

•	A cracked case

•	Case porosity

2. Replace the faulty case half. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - NVG 120-NR9 Unit Repair.