Well, all plastic rads are subject to wear, and will break at some point.
It's common on Japanese cars. We use MB coolant in ALL our cars. We recently replaced the rad on our old 1988 Mazda 626. The dealership couldn't believe how long the rad lasted. Many of the mechanics have started using MB coolant in their own cars after seeing our 626.
I don't care why it works. It does, and costs little extra per mile, so I use it.
As to temperature, MB is one of only a few makes that has a REAL temp gauge, so ignore what you know with other cars.
My 1998 C230 reads a constant 83C at highway cruise with the AC compressor only pushing 2.5 bar at an ambient temp of 10C.
At an ambient temp of 32C, with the AC compressor reading 16.0+bar, my coolant temp reads about 97-101C, falling if highway speeds are reached consistently. Not much below 87C though.
Our 1998 E300 reads pretty much the same. Most late model MB's exhibit similar temp behaviour.
1998 C230 "Black Betty"