Sorry, I still have the white out pkg but re-done on the exterior rails only.

I believe the old stuff has to come off, to Bare metal, since the powder is held electro-statically to the part as it goes through the oven, I could be wrong, but this is what my suppliers have told me in the past, and I have seen some items where they did a poor job removing the old before re powdercoating, and it looked like chit!!!!!