Like Nate said, the passenger side is in the CAD housing and you do not need to pull the diff carrier to change it - only the pass side hub and axle.
Before you go to that trouble, why did it start leaking and when? The reason I ask is that the specs on front axle fill is 1/2 inch below the hole. Many folks change it and fill to the top, which causes lube to weep from the seals until the level drops. Maybe you just did a change?
Another culprit is the puke (vent) hose that comes off the CAD housing and goes up to the inner fender under the airbox. If this is clogged the front end will pressurize and force lube out. Make sure the plastic vent cap at the top is clear.
If all else fails and you do have to change the seal, if it were my truck I'd do both seals and also the u joints while I have the axles out.