I had good success so far when rebuilding vintage saws that have serious pitting. First I totally disassemble the saw parts, media blast the affected areas with crushed glass and then boil all the parts in soapy water for 20 mins or so. Rinse the area really well with hot water and as soon as the parts dry, usuall less than 5 mins I prime paint them with etch primer. This has to be done as soon as the parts dry enough to allow the primer to adhere as magnesium starts to break down rapidly after exposure to the air. Then I fill in the affected areas with a type of body filler known as White Lightning but any epoxied base filler will do. Sand the filled areas down smooth and immediately reprime any bare metal, you can still apply more filler over the primer if required until all the low spots are filled in, just don`t leave the magnesium exposed to air for very long before covering it up with either filler or primer. Apply the paint of choice to completely seal up the affected areas.
