Well, no offense to Tom, but from the way you worded it, you have the seal leak like everyone else. But maybe Tom is right, I dunno. I just never heard of the diff covers leaking on our VXes. But several people have the seal leak. Basically, its where the axle housing is connected to a flange on either side. There is a seal that seeps in there. Both sides on my VX are all wet, but only one side drips.
EDIT: I just went back and re-read your original post. Maybe Tom is right. When you said "the gasket between the two sides" my brain immediately thought of the seals on the axle flanges. So Tom is more likely to be correct here. (Sorry, Tom!)
Bart