thanks for the tips, I was trying to think of a caustic that would etch the aluminum without attacking the steel.
Whatever I do, you can bet I'll use anti sieze on the threads. I also have alunox for aluminum stuff (similar to anti sieze but made for electrical work and antennas that use aluminum).
I will try heat before giving up. I don't recall if there were signs of any leaks on the hoses, oddly I have replaced them on 123's they seem to get attacked from within and the rubber seeps oil. The 603's I have worked on don't show that kind of failure maybe they found a better rubber by 1987.
While I've got the cooler lines out I plan to R&R the starter, and maybe put a "new and improved" gasket under the filter housing, well on second thought the adage "leave well enough alone" has taught me something on this car, the first real money pit I've owned
Oh yes, what about tapping the oil cooler and putting a drain in it? Like a petcock or something? If the end ranks are brass I might solder one on. I had a 115 300D that came with a drain plug on the oil cooler, I like that feature it lets you get more of the stagnant oil out when doing an oil change.
PS
Here's a link to the story on the $400 car:
By it so I dont 87 300d $400