As you've already discovered, leaks are #1. The damage they can cause if left unattended can be significant.
In addition to pressure water leaks, you need to make sure that all roof penetrations (skylight, vents, clearance lights, etc.) are adequately sealed. Then there's the dreaded Winnebago windshield leak issue. I'm not sure if it's a problem with your vintage rig but check out some of the existing posts on the topic. IMHO, for all of the above, Eternabond tape is your friend. If you have drips inside your windshield, put a strip of Eternabond over the top edge of the rubber moulding on the outside top of your windshield and make sure your clearance lights are adequately sealed. Hopefully this will fix it.
Winnebago publishes sealant "call-out" sheets that will tell you what sealant to use for each application. These only go back to 2000 but they don't change much:
Also, here's a good resource page on Winnebago maintenance, etc:
In searching this forum, it's best to use the Google search box near the top of the page. It's much better than the search function below it.