[Z06vette]

Its a bit hard to tell from the pic where it starts, but it looks like its wet above the valve cover. The oil pressure sending unit stock one or possibly where you installed an aftermarket sender?) can leak. Its easy to crack the factory one when installed the engine- its bumps the firewall and gets cracked. Is it running down the back of the motor or is it concentrated just around the valve cover and wire loom pictured?