Leaks in Class C front cabover areas can be coming from four places:
1) The forward facing cabover window. Brainstorming ... this could inexpensively be replaced by a "blank" or "plug" made of a shaped piece of white fiberglass glued to a thick plywood backing that is held in place by the original window's frame that pince-clamps (with screws) on both the inside wall and outside fiberglass surrounding surfaces. Seal this pince-clamp frame thoroughly as you reinstall it using the best stuff you can find - then all around this frame's outside perimeter edge seal it again with 4 inch wide white Eternabond tape.
2) The five(5) running lights. I removed mine on our Itasca, Eternabonded over their holes, and put them back in without reconnecting the wires (to eliminate water seapage along the wires) so they're still "there", but completely sealed and non-working.
3) The side, top, and bottom cabover fiberglass seams. These are easy to keep properly sealed using the recommended sealants from Winnebago's customer resources documents available at their website.
4) The side windows. These can easily be kept sealed properly as above.
Have you thought of asking the Winnebago factory if they take filler-work like replacing your cabover with a solid fiberglass piece? Of course their factory workmanship on a small (to them) rebuild project like this would be superb and hence done properly. If you like your rig, you might consider putting the "few thousand dollars" into it that Winnebago might charge to really add years of reliable service to your Class C.
We love our cabover area, as it gives us two permanent queen size beds - which we use all the time - and a shaded cool front cab area when traveling. We also store a lot of flat stuff up there at the head and foot of the bed (so we don't have to move it to use the bed)... like a light weight aluminum folding outside table, a folded outside lounge chair, a 12 volt Fantastic Fan for warm weather, books/maps, etc..
