How old is the radiator?

If its original don't tighten it you could break the neck. I'd replace the radiator, heater hoses, and flush with MB coolant. Then forget about it.

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1969 280SE
2027 Ram 1500
2026 Genesis GV70
2007 Tiara 3200
1988 Egg Harbor 37
1981 Boston Whaler 17