Adding Differential Oil

[jimk]

From the 5 ton lubrication order(LO 9-2320-260=12 March 1979, page 28, note 6, emphasis added). M35 is similar.

Change gear lubricant only when required by maintenance repair action, or if contaminated
by water or other foreign material. Drain only after operation when hot. Place vehicle in level
position. Remove drain and filler plugs from case, and after draining reinstall drain plugs. Fill
axle differentials, transfer, transmission, and power divider (M816 wrecker), within 1/2 inch
(12.7 millimeters) of filler plug opening, when lubricant is cold, or to plug level when hot. Fill
other gear cases to plug openings at all times, and install filler plugs

 

[91W350]

The front of the transmission has no seal and/or if your rear seal leaks oil into the bell housing, it needs to escape. Otherwise the clutch will get oil soaked. Most of the dirt will vibrate out of there, it is a dust generating spot anyway as the clutch facing wears, the residue is otherwise trapped in the housing. Glen