Don, your problem involves a risk/reward philosophy. A Rube Goldberg fix may work indefinitely, or when/if the radiator upper hose connection separates from the radiator at highway speeds you may be facing extensive engine damage/repair. I understand your reluctance to replace the radiator ... at $500 online that's reason to pause; however, peace of mind is priceless. The upper hose connection on our 1991 300CE developed a circumferential crack and came apart while my wife was parking the car. The remaining stub was long enough to accept the radiator hose so I could drive the car a short distance home ... replaced the radiator before driving the car again. It's an easy DIY job on a 300CE ... probably a bear of a job on a 500SL.

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Fred Hoelzle