Hey neighbor!
'89 300se
65-98 F ambient runs 80C city and freeway.

'95 c280
65F ambient runs 85C approx to 90C approx. in
city and 80C on freeway.

The 300se has more open space under hood for
ventilation and does not retain the heat
so long after shut off.
The c-280 is cramped under hood and gets HOT
in there as well as retaining heat long after
shut off. This is probably one reason that the
wiring harnesses begin to deteriorate besides
poor design of insulation.

Maybe your radiator needs renewing of fluid
with less antifreeze.
Try redline waterwetter combined with less antifreeze in the mix.
Keep an eye on it!

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1979 300D
133K miles
1989 300SE
1995 C280