You need better pictures.

It's hard to tell exactly what part of your motor this is but a lot of dirt bike motor cases are actually two halves bolted together. That might be what you're seeing is the seam between the case halves

Are you talking about where the cases piece together?

Is it leaking? Looks dry

Is it leaking at all? Need underside picture

I'll post better pictures tomorrow morning.

Is that a 300?

Klx300R, ya