Radiator age is in issue, because if anything other than distilled water was used the buildup and effeciency loss could be huge. Any leaks cant cause boiling. A new thermostat is always the first guess as they come bad out of the box, buy OEM there. Burp the system, dont overfill reservoir. If the fan clutch stops easy with a rolled up newspaper while running you can put new oil in it. Check on Benzworld.org. I was able to refill mine.

Good luck.