Join Date: Mar 2009
Location: Kelseyville, CA
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Bondo makes a plastic body filler with fiberglass in it called bondo-glas. It's fine. Fiberglass cloth is still the stuff. The best repair is still to weld in a patch, but you still have to blend it with body filler. The key thing to know is that when you don't have a metal backing, you must use a plastic body filler rather than one based on gypsum. That's because otherwise you'll draw moisture from the back side, and the moisture will spread throughout the filler and then rust away from the surface.
For small holes you can clean the area and remove all rust, then prime the area and then apply plastic body filler over that. Some will say body filler should always be used over primer, some say never use it over primer, I say follow the instructions.
Is the paint actually clear coated? If so, then yes, you color match and then re-clear. First you want to use 500 wet or similar (for example a green scotch-brite) to dull the paint all around the affected area, larger than the area you will be spraying with clear. Then sand the paint with 180 dry on a D.A. (that's ideal anyway) to a feather-edge, spray primer if you have any metal to cover, and then spray your color, then your clear, with appropriate dry times between coats.
If the paint is actually a single-stage, which can look like it has a clear coat but is very thin, then you just feather edge and spray. You can use a little clear coat applied correctly to match the finish. If the finish is dull then you spray far from the surface so it comes on "Dry", etc etc.
Typical sealers used for auto body seams of the era include butyl and mastic. I like a stuff called trempro 636. I get it from vintagetrailersupply. it is low- or no-voc depending on how long ago it was made, it has a nice long dry time, and you can apply more of it later unlike silicone.
1992 F250 XLT 4x4 Super Cab 7.3 IDI E40D 3.55 ATS 088 4"R.C 360k
1982 MBZ 300SD W126 California model w/Sunroof, no EGR
1997 Audi A8 Quattro 225k Warm/Cold packages