I just received an email from 3M customer support. The 08509 has been discontinued. I’m going to try this product that I found on Amazon:
C.R. Laurence CRL7708 CRL Windshield and Body Sealant. It sounds like a similar product and people seem to be using it successfully to stop windshield leaks on older cars.

My dad always told me, "Don't force it, get a bigger hammer".