I guarantee that there is no way that a 420SEL is going to get 23mpg in the city, so that has to be a highway rating.

My '95 E320 gets around 25-26mpg on the hwy and dips to about 20mpg in town and that is with two less cylinders and 1000cc less displacement.

Car looks pretty nice from the pic.

You need to see in in the skin to really properly assess the car and of course drive it.

Check eBay and autotrader.com to see what kind of money these cars are getting.

Regards - Yasin