The factory used a "dam" and Thiokol pumpable adhesive with different silane primers on the glass and on the body opening flanges, which changed to urethane pumpable adhesive in the 70's. GM never used butyl in production, as it won't pass the MVSS 208 Frontal Impact Windshield Retention requirement, and the Thiokol or Urethane adhesive design makes the windshield and backlite structural parts, improving body torsional stiffness. Some glass shops use butyl for replacement glass because it's quick and cheap, but it's technically illegal. The factory rubber spacer blocks established the windshield height for correct flush fit of the reveal moldings to the glass surface.
