70 chevelle ss rear bumper question

[Schonyenko2]

If you have the new style, they're made out of a kind of slimey rubber/plastic that feels slick to the touch. You need a special adhesive to get them to stick right, and it doesn't work that well. Last I knew, Year one, or OEM had it. I seem to remember there being a short shelf life.
Originals usually stick pretty well with most good adhesives. Sometimes a little super glue in the corners will hold a long time.