If not too late, I would suggest you fit the seal joint top centre and, if possible, close the joint in the rubber ends with a suitable “superglue” to prevent it opening up and allowing water ingress at some future time.
If you also cut the overall length slightly “generously” rather than tight, it will discourage the seal from leaking should it contract – but beware, I don’t think there will be anything to retain the outer profile of the rubber and too big could leave it loose on the glass possibly leading to different sealing problems. Ain’t life simple!
B…..
Bernie