I have been driving one for several years now, with close to 200,000 miles on the odometer. I have had several pricey repairs, but the car has never left me on the side of the road, and I have never ever felt unsafe in it. Last summer I drove 21 hours straight from Halifax, NS to Hamilton, ON, including stops for meals and gassing up, averaging 70 mph and had absolutely no problems. That's 1250 miles in one day. I am planning a trip from Toronto to Orlando to Halifax and back to Toronto this summer (about 5000 miles I estimate)and I am looking forward to letting my 420SEL stretch it's legs. I can't imagine a car I'd rather drive, in fact I would love to have occassion to drive my car as much as you will be driving yours. Have it inspected at a Mercedes Dealership and if they say it is in good shape you'll be great!
If you have any other questions feel free to ask or email.
1995 E420 - retired
1986 420SEL - retired