I have owned all W126 Gas models. The 560 is by far the best one for me. As others have noted above, find the best one you can afford that has been well maintained. Mileage is not so much of an issue with these cars just as long as maintenance has been kept up. Repairs are not cheap, even if you DIY since quality parts come at a price. My current 560, a 1991, my father gave to me 3 years ago. It drove just ok but he never spent all the money needed to make it decent. When he handed it over to me, I spent over $5k in repairs for the Transmission (Lost reverse gear. Common issue) , Timing Chains & Guides (way over due for replacement), Front end Steering/suspension, rear SLS suspension, Vacuum lines and rubber hoses, radiator, tires, reg maint (filters, oil) etc...

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2001 E55

2001 E320 Sedan

2001 Subaru Legacy

2006 SLK280

2016 Subaru Outback 3.6