"So Tom is more likely to be correct here. (Sorry, Tom!)"
No worry. I put it on the calendar so no one would ever forget that Tom was RIGHT, Bart was WRONG! It was bound to happen sooner or later.
You were right in that I don't recall anyone here ever mentioning that their diff cover was leaking. Several have noted that their axle seals leak though.
We'll just have to wait for the pix.