I ran into the same problem when resealing my 66 Mustang windshield.
I found that 3M no longer will sell to consumers and parts stores don't want to have a case of this stuff go bad if not sold within two years.
I used C.R.Laurence CRL7708 Windshield and body sealant for my project.
It does not solidify and cleans up with kerosene or mineral spirits.
Plan out your install because it is very tacky, like pizza cheese, and will string all over your interior if you are not careful.
I did my install on May 12 and it is still tacky on June 19.
I bought my tube of CRL7708 from Summit Racing at their store.
