The W210 E300 is the closest to your current beloved W124. It is extremely reliable and gets better gas mileage. Its only weakness is the glow plugs. Carbon builds up around the tips and makes removing difficult and sometimes they break off in the head. Mercedes created a special glow plug removal tool for this. If you replace them every 100,000 miles you should never have a problem.
This would be a nice transition car with mostly mechanical and a some computers thrown in.

Mark

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91 300GD SWB with transplanted 87 OM603 turbo motor