I would start with replacing the turbo intake seal (big orange seal inside the black pipe) as well as the crankcase breather pipe seal, $30 in parts tops. Then clean the intake valley with degreaser thoroughly and flush with water.
My 2008 was diagnosed with a bad rear main seal 5 years ago, it was just the crankcase breather and turbo intake seal which I have resealed twice now, I goop it up with perma seal gasket sealer and a new seal each time. Never touched the oil cooler to date which the dealer always claims is at fault, but I have never had to add oil, just a drop visible on the bottom of the bellhousing at times. I do smell it burning off the exhaust on a good hill climb...
I am under the impression there is so much stigma attached to the oil cooler leaking that it is done regardless of the source of the leak, and since the turbo pipes are part of the job anyways it ends up being fixed. Yes, severe leaks are usually the oil cooler, but minor ones tend not to be. I have a nice flexible LED light I shine down into the intake valley to look around when changing the fuel filter, you can get a good look around (not all the way to the oil cooler but enough to see if there is oil pooling down there). These engines do have a good amount of crankcase blowby which if leaking can really drip a lot.