I thought this article on "beaters" that called the W123 "Quote Possibly the Most Durable Cars Ever Made" would be of interest to people here.
http://www.beaterreview.com/?p=45
My personal experience is just as favorable. I've owned my 1983 300D for just about 3 months now and it's been a blast. Frankly, I'm partial to older Mercedes and this one is just modern enough to drive every day.
Doug
P.S. I posted a similar link to this article yesterday and it was deleted. I'm guessing someone thought this was spam?