I had the same problem on my 94. Not an issue if all the same oil. It does become a pain though. I fixed mine right away. No way I'd have delt with it every 50 miles!
I didn't ride much, couldn't sell it because I would not feel right unless I fully disclosed the problem, then the price would be too low. So it was a paperweight. I haven't been back to the guy that rebuilt it and left me with the problem. He had told me at the time that my cases were fine. After I got it back with t hat problem, he told me a the cases were bad. I didn't have the money for new cases, so that's why I had the problem for 3 years.