Interesting post with a lot of good information. We have 2003 Jayco 25ft motorhome and the only place I have found a leak during a four-day heavy rainstorm was on the top of the slide where the waterproof tape had rubbed off when it opens and closes. After the trip, I cleaned it up and retaped it tight. I inspect our roof, clean it and caulk it each Spring. I inspect the inside ceiling and windows edges each month and after each heavy rain or snowmelt. So far, so good.
I do have windows on the front cab, and I inspect them monthly as well. I like the windows as we live out West and most often have wonderful views from all windows.
Leads are inevitable at some time on any rig. But checking them often catches problems early and doing regular roof maintenance helps.