This leak that has bugged me since I got it when it gets cold out wasn't my oil cooler. It's the front cover. That's nice. It sure looked like the front oil cooler header. I'm glad I have another engine that I'm rebuilding because this one is driving me nuts!!!
It's leaking right behind the front header at the engine cover gasket on real cold start ups. I can't figure why since that isn't a pressurized place on it but that's sure it.

 

Glad you figured it out....just sucks all the work you've put into r&r'ing the cooler all this time!

 

I know. I'm not even trying to fix this. I'm just going to work faster on the new engine. This one has had it. The last owner got ripped off by so many wannabe mechanics on this mess. I just give up. I've pretty much got a new truck now with all the work I've already done. In a couple months the last part to make it all new will be in.