Internal flare can be reduced and contrast improved with these fast lenses by carefully
blackening the element edges right up to the polished surface. Very often factory blackening
has flaked off or is otherwise incomplete.
I have a Raynox Polaris 135mm f1.8 with what appears to be a paint flake near the outer edge of the front of this triplet. A paint flake was all I could think of, and that must be what it is. I just might get up my courage to go in there and take the flake off and remove those pesky dust pieces, too. Then paint edge like you say.