oily substance coming from 135 hp omc

[RidgeRunner]

My 90 Johnrude did that very same thing for many years. I premixed and ran fat on oil all the time. I was under the impression mine was exhaust pushed because it was more burnt than yours appears to be.. I never was worried with it. I was attempting to go after a rusty swivel bracket on that motor, so I had the powerhead off. I replaced the base gasket and the annoyance of that "oil" was gone once and for all.. That was a fairly cheap fix as I had a gasket laying around.
BTW- The burnt goo/oil leaking out of the lower unit around the prop once led my mom to believe the propshaft seals were bad, so she had them replaced. She drove the boat to the mechanic by water. The mechanic let the boat get caugh under the dock and screw up the gunnel on the port side. I had just replaced the gearset,bearings and seals in the lower two weeks prior. At two weeks old the seals were fresh as a daisy. What a PITA that mechanic was, he saw an easy mark in my mom and took advantage. She was just doing me a soilid, she didn't know any better. Another one of those moments in a boaters life..