Hey FTE! My first post here, but I have read a lot of info from y'all. I just could not find a post which directly related with my question.

Please bear with me here:
I am buying a 2007 diesel with 145k on it. It runs, drives, and starts fine. There is no oil leaks underneath and appears to be in mechanically great shape.

However, I opened the hood, and noticed that, around the degas cap, there was some residue (simply bad seal, or blown head gasket?). The coolant residue was not on the hood or anything, and the wells around the heads are clean. And having experience with a early year 04, I got real gun shy, and asked the owners to run a compression test. We brought it to a local diesel guy, and he ran the codes, and came up with a low egr flow code (not sure the exact one but thats what he said it was). Also, he said there was low compression in coolant bottle (around 9psi).
So he pulled the egr valve, and it was sooty, but not caked at all, and he looked down into the hole (cooler?) and said the truck needs a egr delete (This is in FL, no emissions). He attributed the coolant overflow to the turbo pressure backing into the coolant, and because of this caused the overflow.
He is going to install a welded egr valve in, not a sinister or anything like that
So at least the compression in the bottle was not over 20psi (bad gasket probably?)

Does this diagnosis make sense?

Thanks again!
-Adam

 

Minor leakage that I saw, not splattered on hood though

 

Has any damage occurred to the engine by driving around with insufficient flow in the egr valve?