Mercedes decided to use plastic radiator tanks glued and crimped onto an aluminum core. It was light, thermally efficient, and cost effective, but the problem was in the neck of the tank. The neck was subjected to intense heat and vibration two things that plastic hates. The necks fail frequently. If you have ANY cooling system repairs done in the future no matter the mileage of your car have the tech pull the upper hose off of the neck and inspect it. If it has an aluminum insert inside of it it's OK usually. This means it has the updated tank. If not have it replaced you are ridding on borrowed time!!
All 1984 to 1994 (roughly) Mercedes.