I've owned two 124 cars, an '87 TD wagon and an '93 2.8 sedan. Both cars in Dallas, so a little bit of summer heat. Based on my experience, your coolant temps are normal and not a concern. Both my 124 cars would run 90+ on the highway in summer heat. Both would reach 105 in stop and go driving, with the coolant temp slowly falling while driving at city speeds.

My opinion - you're obsessing over nothing.