Hard for me to tell with the photo.
I would suggest a very deep cleaning with good degreaser, then maybe some other cleaner like Simple Green or such.
Lots of rag usage, even small soft brushes. Get it spotless. Then keep an eye on it.
Do not just clean that spot, clean the entire engine front to back, top to bottom, then consider doing it again.
Even a slight seep somewhere can travel and make it look bad.
Also clean the coolant lines.