CReeves,
You can take this suggestion for what it's worth, but I have used a product (K&W Block Seal) over many years in the past and have been amazed at how well it works with regards to internal and external coolant leaks.
It was recomended to me by a friend (also one of the best auto mech. /fabricators I've ever worked around) years ago.
I have never used it on diesels, (only gas) but it has saved my ***** many times, never failed me, and never had any neg. side effects. ( Cooling syst. clogs etc. )
I have not bought any for years,but I'm sure it's still available, I think I might still have a can in my garage.
For $12 or $15 per can you might consider giving it a try. I would be very curious to know if it works.
If you want, PM or call me and I can tell you some things I've done with this stuff.
Best of luck with this problem.
Ray