If your problem turns out to be the windshield, check out 4Crawler's site for a repair using vinyl baseboard trim. I did it on my Toy motorhome, which leaked badly (floorboard puddle) and I don't think any water's gonna be getting thru for a long time.

If one removes the stock windshield trim when doing that repair, it seems that the removed parts fetch a nice price on eBay.

1986 Sunrader Motorhome 22RE $200
1987 4Runner 22RE (under construction) $80.77
1989 4Runner 22RE, 6" lift, 35" Dunlop mudders $420
All rescued from sitting to death, all auto, 'cuz I'm too dumb to drive a standard.