A couple of years ago I replaced just the top tank (plastic top) of the radiator in my 300D. Found a company that supplied the tank and seal for about $25.00, then couldn't find the information again when others asked.
Just found the info that I had printed out and filed away in the garage.
Don't even know the name of the company but the phone number is 1-800-328-8900.
As I recall, I called and advised year and model of the car and the customer service rep quickly identified the part and shipped it right out. (This after the plastic neck for the top radiator hose broke off). Anyway, thought I'd post it here in case others need it.
Cheers all. fmb