Steam & antifreeze smell could very well be the heater core, or maybe a leaky coupling. In either case I'll guess a major portion of the dash has to come out.

From what I've seen, very little repair work is too difficult for someone of normal skills and ability at-home, provided you've done it a few dozen times, and have a hydraulic hoist, engine puller, brake grinder, tire mounter and access to a good machine shop It's the training and experience that set the techincians apart from us mere mortals

When I saw what the technician removed to replace my AC evaporator in the Audi I realized I won't live long enough to get that kind of DIY experience.

My vote is for you to have a dealer/independent MB shop look at it and get a quote.

BCingU, Jim