There is a misconception that the bond is mechanical, hence the need to sand heavily. The bond is more of a chemical nature. Whay I have done in the past is use PPG DP40 primer, PPG urethane hi-build surfacer, followed by sanding down to 600 grit wet, followed by thinned DP40 as a sealer, then a direct-gloss urethane (PPG Concept) top coat. Basic removal of silcone and waxes prior to knocking the gloss off the paint is all that is required.

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'96 C280 (gone)
'97 C36
'05 C230k