There should be a gasket??

[turbojohn]

The front differential bolts up to a large piece of what looks like a skid-plate and frame cross-member. Sorry I don't know exactly what it's called, but it's leaking out the bottom of the differential, where it seals against and bolts up to this skid-plate/cross-member.

 

[Will]

A 1/4" bead of orange silicon. There's no gasket. Put the glue on the diff and then carefully set it in the axle beam.