Any mileage representation on these cars is meaningless w/o complete records, meaning year-to-year for at least most of its life. Those odometers are 5-digit as pointed out and every one of them breaks, meaning 99+ out of 100. I've forgotten how many w108 cars I've owned, (4?), and worked on quite a few others.
From a practical/driver standpoint, the biggest issue with that particular model is that it is carbureted and certain carb parts are NLA. They tend to be difficult to keep running great on today's gas and carbs simply wear out after 40-50 years. From a valuation standpoint, the 4-door cars are plentiful and cheap in great condition. You may see people asking a lot for them but unless they are in truly showroom condition, they sell cheap if at all. It is very easy to "invest" more than the value of the car in repairs in the first months of ownership if they have mechanical needs.
On the plus side, a nice example is a lovely car from a time when Mercedes-Benz cars were beautiful and made to last. It is not a car to restore in any scenario, you can buy the best one in the world for a fraction of the cost of a proper resto. I've owned them in jaw-dropping condition and they sold for mid-4 figures.
