as some one described the casting location:
"The casting number is on the drivers side, near the front of the engine between the first and second cylinders at the top. You will find a MB part number in the format 603 016 XX 01. The XX is the casting number"

A heavy fuel smell? I would suspect the inj pump or timing way off. Does the engine have any nailing sounds when idling?
If it smells of antifreeze that would make one not want the car, ok, well maybe it just needs a head gasket but with so many failed #14 cyl heads, that would drop the cars value pretty fast if white smoke that has that characteristic sweet smell its going to be costly.
If you have a mechanic that works for cheap (or can DIY) and a few thou$ to buy parts and if the rest of the car is really fine then its probably an investment worth thinking about.
OTOH, I have two W124s w/ #14 heads and still running strong. I did have the top end rebuilt on them though. There are still plenty of #14 N***ty heads still running at well over 300K miles.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!