It seems like the OP has been edited but it was originally suggested that the radiator needed to be replaced, and that cost would be $1400.So far, I can't see what the dealer has done wrong. The radiator is caked with debris, which the owner has verified that there are portions that he cannot see light through. The dealer has said the oil doesn't look right.
What would you expect a mechanic to do in this case? Not tell the customer? The OP has not elaborated on the $1400.00 repair mentioned in the title of the thread. What does that include?
And by the way, in my experience it is common for debris to cake on the back of the radiators. It seems like dirt and dust (especially when moisture, antifreeze, or oil is present), get flung by the fan, and stick.
As for what I would expect the dealer to do in this case (I realize your question was rhetorical to the whole group but I'll answer anyway LOL), I would expect the dealer to give a quote for cleaning the radiator rather than just saying "looks dirty, you need a new one". Add to the fact that the OP claims that the engine was not running hot and had no indication of a performance issue while using it....this all seems like a lot of projection and assumptions on the dealer's part to get a $1400 radiator sold to the OP. But I could be wrong <shrug>