Windows can and do leak. The older the van, the more likely these windows have needed work, and not received it. Personally I would avoid buying any vehicle with visible water damage because you never know what you can't see.
2021 Promaster 1500 118wb conversion
2019 Roadtrek Simplicity SRT (almost a Zion)
2015 Roadtrek 170
2011 LTV Libero
2004 GWV Classic Supreme