Just pulled the axles for a gear swap and one of the axle gaskets ripped. Is it ok to use ultra black silicone in place of the outer axle gasket? Called all the auto parts stores around and no one has it in stock...and I wanted to get it back together today.

That'll work. Actually the axles didn't need to come out all the way for a pig swap. Wrap a piece of brown grocery sack tight around the splined axle end then insert it in/past the seal then let the sack loose & pull the sack out so the splines do not contact the seal. Do this on axle removal also (assuming that the seals ain't being replaced)

call cass (dr.diff) he'll have everything you need - great guy.

ultra black better than the flimsy gaskets

I save the thin foam packing material to cut those gaskets out of.

They aren't sealing oil in, they're just keeping dirt out.

R.