Because of the construction of these radiators: aluminum core and plastic tanks on eithe side, it is VERY difficult to rebuild them. My understanding it is the actually attachment of the plastic tanks to the aluminum, where it is an art, a hit or miss.
I recently went through this with the 300E. I called several radiator shops and inquired into rebuilding mine. Three shops refused to do it unless I would decline any sort of guarantee from them. I have heard that there are shops that figured out how to do it, but for me the only way was replacement.
Additionally, the weakest portion is the "upper" neck where your upper radiator hose attaches. These tend to get brittle and break. The "new" radiators have reinforcement inside the necks to help them from breaking.
From everything I had learned and read, the way to go is to get a new one.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)