Originally Posted by
EvaDestruction
Isn't it called 'exfoliation'?
Not quite. Exfoliation is a severe form of intergranular corrosion that starts from a manufacturing defect. While there maybe trace surface corrosion in the OPs picture, the majority is erosion damage from flying in rain. The WD40 part you remember is the weekly blade inspection recommended by Bell which usually includes dressing the leading edge so you can apply the WD40.