Iben
Most new Mercs of that vintage were owned by quite wealthy people and be assured most of those people were NOT diy types.
Those Mercs typically had more money spent on them in the form of routine maintenace and repairs, than would be spent on most other marques,
over the same period.
So, in conclusion the high miles achieved have been achieved due to massive expenditiure in most cases - so do not be misled into thinking it has all come about through some magical build quality and abnormally good engineering.
That continues to be the situation ongoing, you just cannot neglect maintenace and repairs, and it all costs money, unless you are into diy, which many forum members are.