On my 76 I used the 2x rustoleum, found a color that matched the OE saddle color perfectly. I scrubbed them with soap and water then right before I painted them wiped them with some denatured alcohol. Light coats and let fully cure before reinstallation.
This is how it has held up with a year and a half of daily driving.
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It hasn't worn terribly considering that these door panels had completely sun faded and become brittle and turn into dust. The areas where it has fallen off is where the plastic underneath has come off.
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I also did the dash pad cover, same prep method, has held up excellently as the plastic isn't degraded
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