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The M120 is just two M104s on a common crank, so the complexity is having 2 mafs, 2 etas, and 2 ecus. Admittedly, thats potentially a nightmare if they need replacing, but (urgently looks for wood to touch) in 20 years of owning cars I've never had to replace any of those items in any car.
Nappa leather is the main difference in the S600, though most also have the electric reclining rear seat including the electric head rest up/down, Multi contour front seats (As opposed to just lumbar) 4 zone climate control with seperate blower motor for the rear, heated rear seats (Thats maybe on all models?). Mine also has a dinky little fridge between the rear seats. I think the S600 also got the half walnut steering wheel which was optional on other models. And most pointless of all, a button which changes the rear seat[/CODE]adjustment switches to control the front passenger seat instead. The S600 is also only in lwb, where as all others were available in either regular or lwb.Code:[CODE]
Much like the w126, there was an option for individual rear seats which was quite expensive. Despite losing the practicality of having 5 seats, and the fact I'll probably never ride in the back, I still think it's a cool option.
As with all MBs of the 80s/90s there so many options, finding identical cars (other than taxi spec) is near impossible.
If you don't mind LHD there are some S350D models floating about with the 3.5 turbo diesel om 603, and the S300D 3.0 turbo om606.
Thanks for the detailed reply, and the performance?