I'm not sure if yours has an oil cooler, if it does, make sure it's doing its job. I recently replaced the heater core on my 1970 280SE, which had been cooked due to a higher-temp thermostat installed eons ago, the oil cooler lines disconnected at the oil filter housing, and a once-faulty fan circuit. Everything's now in working order, new heater core and oil cooler fabricated from scratch, lower-temp thermostat, and new MB hoses and pipes reconnected.