Everyone I have were destroyed when pulled. Most windshield replacement company's will sell you the piece for cheap...
When I had a leak in the past it was mostly on the very upper piece you are talking about.
Most of mine were from rust where the ceiling meets the windshield(be careful ..if there is rust ....you can make things a whole lot worst when taking out the top molding)
A shabby backyard windshield replacement job was the cause of the other leak. You should use special windshield sealant as it works GREAT and sticks.
Once I just had a small wind pressure leak on the side and used standard clear silicone to fix it.
Hope this helps. ......