I get an overall 25 MPG on my 300SDs The 300 SDL (six cylinder) seems better but I haven't had it long enough to get an overall average.
The 300SDs are very reliable and the engines last forever. The biggest problem is body rust if you drive in the salt that the idiotic DOT puts on the roads. But this is a problem with all cars.
Try Ebay, there are usually a couple for sale there.
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