Trailbeast is correct. The 40 year old material is now hardened and reluctant to change (like some people I know). The important part is the use of a heat gun to soften and stretch the material. I wouldn't use steam as that would make the material wet. A steamer is good for headliners. Pull up the old stuff, heat and slowly work and glue. All this being said, nothing looks as nice as a new panel.
