I have been cleaning up some aluminum parts lately and A Harbor Freight soda blaster with baking soda medium will make short work of that part..It will blast away the calcium but is very easy on the aluminum it self

HF sell the baking soda in 50 lbs bags..And you can't believe how good it works on greasy parts too..

I think that what you will find after you clean it up is holes through the area where the radiator hose clamps on..But if it is not to bad, it might seal when you reinstall the radiator hose

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1978 300SD 303400 miles
1983 300D 341270 miles
1980 300SD 320456 miles