Looks just like my pipe.
Here is a link to the Screwed Nipples repair.
http://www.peachparts.com/shopforum/2743295-post2.html
We are getting off base here from the problem the OP has. I was looking for a thread where I saw a picture of one that got tore off. can`t find it with the way the search is now.
An Oil Cooler from PNP is about $20, and the time to pull it and drive down there and back. for me the closest one is 50 miles round trip, so $50 or $60 really isn`t unreasonable for a used one.
I would just replace the cooler instead of welding it.
Charlie