Looks to be too straight for a die crack. They are usually irregular lines. Might of been struck through some debris. Reverse shows possibly some debris. I do not like to use the word grease. It could be many diff. things beside just grease.
It is a small delamination. No added value, laminations/delaminations are fairly common on nickel alloy coins. A large delamination, one where a significant portion of a face was missing, would garner a modest premium.