It drips down the line and collects at part 11 (oil cooling pipe).
At least on my truck, that was the problem. Here is a good look at the part.
Image Gallery(ES:37560): Thermostat
Mine was leaking around the metal clip. I guess the seal was made lose when I was replacing the big radiator. Mine was leaking exactly like yours.
I don't think the oil cooling pipe inlet is the problem, but I really can't tell since I am not there.
I ordered the part to replace it, but it stopped leaking on its own. I guess the seal formed back somehow.
Good luck