Originally Posted by orangef4
If it's just on the metal, it's corrosion. Just clean it up with some steel wool or similar.
DO NOT use STEEL WOOL or metallic grinding of any kind!!!!
If it is an HEI, or other Magnetic Pickup type of trigger, You will end up with slivers of steel stuck to the magnetic parts and it will trigger all over the place as the rotator star turns! (Akin to having points that fire anywhere they want..)
You may be getting Condensation UP the shaft from the crankcase, settling inside the cap..you just may want to consider pulling the Dizzy and inspecting it for end play and runout..AND while you have it out..Media blast it.