Wow! Took a minute to get the picture orientation sorted out in my mind that this looking down towards the hood! LOL!
That is a crack in the putty filling the gutter. It can be dug out and refilled. The concern is water reached down under the putty or possible down into the windshield channel and is creating a rust situation away from view.
If this a newer van, paint all looks good, no rust elsewhere, van meets 90% of my needs, this would not be a deal breaker/concern for me. If the seller is willing to have tis addressed prior to sale then there are no surprises. If seller is not up for dealing with this, I would carefully inspect around the crack in the putty for any signs of rust, make an allowance for a few hundred dollars to get it addressed either by myself or a very reputable body shop.