Yep, most likely a bad seal between the upper and lower. Its a piece of cake to put in new seals. 6 nuts on the top and a bolt under the lower zinc and its apart. Just drain the lube first.
I never touched a drive till about a month ago. I installed a larger spacer between the upper and lower. It took me about 2 hrs start to finish and 20 mins of that was letting the lube drain out.