I believe the aux fan temp is at about 110c, I remember reading in the performance forum about a mod that owners of the 500e's had done to bring the aux fan cut in temp down so that the cars never went over 100c. They seemed to have a similar situation to yours where a few owners seemed to experience hotter temps than others even though they had new radiators, new hoses, new cap etc etc. I assume that these have all been replaced. Certainly replacing the temp sensors might be worth looking at. Also as I mentioned see if you can get hold of a different guage to be sure that your dash mounted guage is displayed the correct temp. Sounds like a well cared for car - you should post some pics somewhere if you can.

Good luck
Matt.