Theories on rear engine fuel leak?

[Learjetter]

Gang,

AP/IA out of pocket until the weekend. Opened Pilot side rear cowl and noticed blue staining near #3 cylinder on baffle and below #3 cylinder on engine Mount tube. Anyone want to hazard a guess or propose a theory for us to look at? See photos.

Non-turbo, G-model, TCM IO360-G. Running the boost pump on high with engine off did not result in any obvious leaks.

Has anyone had a problem like this before?