3M Bedding and Glazing compound.
It must be applied between the rubber and the glass, and between the rubber and the window frame. It's a messy job.
Also, you must apply it between the header trim and the rubber.
I suggest you make the shop remove and properly reinstall your windshield. Failing that, get a buddy and redo it yourself. There are articles "out there" on how to do it. It's not that bad - just messy. Been there, done that.
I'm afraid that if it wasn't properly sealed when set, you will never get it leak free.