Remove Undercoating
Gasket scraper with lots of elbow grease and heat for the first thick layer. Then WD-40 in a spray bottle with wire brushes and scrapers/knives..whatever works. Then green scrub pads for that final thin layer. Then soap and water, then rinse with water. Then 2 coats of your favourite rust proofing paint like Por-15, Master Series Silver or Rust bullet or whatever. Then a finish coat of whatever you want.
Gasket scraper with lots of elbow grease and heat for the first thick layer. Then WD-40 in a spray bottle with wire brushes and scrapers/knives..whatever works. Then green scrub pads for that final thin layer. Then soap and water, then rinse with water. Then 2 coats of your favourite rust proofing paint like Por-15, Master Series Silver or Rust bullet or whatever. Then a finish coat of whatever you want.