What is this hole for on engine/tranny? Stumped!

[TimR]

Hi all, question on my '00 986, 2.7L.
I was changing air filter and then blowing acorns out of engine bay when I noticed this somewhat oily residue around this hole, and it made me wonder if normal or if it's missing some sort of plug. I'm not an expert on identifying internals, but it's viewed from left rear of engine, just behind the oil (?) cooler. I couldn't get an angle with my camera, but if viewed looking towards the front of the car inside this hole I can see teeth of a gear (timing gear?).
Anyway, figure someones' seen this before and can dispel any concerns.


Thanks all!