I use Mobil One 15W/50 in my summer car and
Syntec 5W/50 it the winter car, both are 300SDs. I change both synthetic oils every 10K miles. The summer car, with 220K total miles, requires no additional oil between changes. I have been doing this for the last 110K miles I have owned the car. I have no earlier records. The winter car, 180K total, uses 2 quarts between changes but seems to be using less the more I drive it. I have been doing this for the last 20K miles.
I also use a PTFE additive of varios brands. If this routine did any damage to my engines, surly it would shown up by now. Both engines run excellent and start readily down to 10 degrees F. I say sheisen to more frequent oil changes.