That is bad advice. Sealed in corrosion just gets worse. Remove the corrosion and prime and paint. you may have to sand into new paint area but paint is the protective covering and can be reapplied. In 20 years of fighting corrosion at sea on multimillion dollar aircraft,I would NEVER recommend sealing it in. One day you will notice a bulge where the corrosion has now worked its way further into the metal.