MY 96 C280 w202 w/145k mi is overheating (in the red zone @ ~120+). The fans are kicking on. when it reaches ~100-degrees so I think those are OK.

The water pump and thermostat were replaced @ ~90k miles
The head gasket et all (incl radiator flush) was done ~112k miles.

I believe the radiator is original but i am not 100% sure.

Any idea where I should start to investigate?

Thanks.