oh dear spent 30 years doing it wrong.( ofc you can reseal a leaking windscreen, if its a pinhole or even a couple of inches we used to do loads under warranty for manufacturers. most times its a case of removing the exterior trim or part of it and with the area dry and primed reapplying bonding compound. if the area can be accessed by dropping the edge of the interior trim then apply from inside.
the only time you may struggle is if damp or rust is present.
for a diy-er i dont know if they still make it but halfords used to sell a clear liquid that you used to squirt in around the trim when dry and use to find the hole and the seal it , have to admit it didnt normally end up being a long term solution but i have know customers who have gone years without leaks reappearing.
cant see it at the moment but it was like superglue without the harmful effects on the paintwork, im sure if you look around you would find something, but as said have a word with yo local small w/s company and see if they can do anything.