[962porsche]

1st test the coating . do this by taking a rag with lacquer thinner on it and wipe just a little area to see if the black coating will wipe off or not .
if it does then sand all of it off with 220 or 180 grit paper .
if not just sand it with 320 grit dry or 400 wet to take the shin off the black coating .
then if you have sanded thru in a lot of areas (sizes bigger then a dime )you would want to spray a coat or two at most of a e-primer over the panel . of not there is no need for a E-primer (Epoxy or Etch ) .

once the E-primer is dry sand that with a same 320 or 400 then just spray a coat of sealer on the panel and top coat doing wet on wet from the sealer .

if you have to remove all the black coating the proses is the same but you will want two medium/wet coats of a E-primer to give more of a mil build for sanding .

there is no need to just a filler primer if there is no body work on the panel . the reason is more product is not good . primers like a filler primer does nothing to protect the substrate in any way . all it does is add mils to the panel . more of any material is always worse then less .
you want to use as little amount of a E-primer as you can so one coat is better the same holds true for your filler primers . when it comes to a filler primer you want no more then 3 to 4 coats . and the same is true for your clear coats 2 to 3 coats (3 coats at most ) .