Tech question for you...

I've got a 96 w202 c280 w/165k mi. Replaced the thermostat ~10-15k mi ago (~18 months) due to overheating. It hass run fine @ ~90c degrees until recently.

Now it runs in the 105c-119c range (not yet cresting the 120c degree redline threshold).

Important info:
Ambient temp 50f degrees
Both cooling fans appear to be operational (kick on and run low then high as the temp raises and are able to keep it under 120c degrees)
This is a 3rd car and seldom is used
Coolant level is OK
No CEL and no Low Coolant lights

What should I look at first?