A few pieces of info on 140 charcoal filter systems.

On the versions WITH the charcoal filter, you will have the air intake slots on the rear of the hood up on top. The versions WITHOUT the charcoal system just had the flat hood, no air intake grille.
Later on, I believe they decided to standardize the hood, and ALL hoods had the air intake (either that or the charcoal system became standard, but I believe I have seen 140's with the slots on the hood, but no charcoal switch), and I also believe that the hood with the air intake hole is the only one MB will sell now, (replacement part hood).

One point to clarify is that if you do have the charcoal filter, the charcoal filter itself is quite expensive (they were at one time around $750, now I believe $500 or so) and a bit of a chore to replace, you need to remove the windshield wiper assembly to get remotely close to it.
The filter above the blower motor on the charcoal filter equipped 140 is referred to as the activated charcoal pre-filter, I believe the cost is over $150. If you do NOT have the charcoal system, the filter that exists over the blower motor assembly is simply referred to as the "dust filter", it is a simple paper element, probably under $30. I believe you could "hot rod" you non-charcoal equipped 140 climate control by inserting the charcoal pre-filter, they seem to be about the same dimension, but the charcoal pre-filter is quite a bit heavier, seems to be also loaded with activated charcoal material.
Both versions us the same recirculation filter inside the cabin, very cheap item, just a pre-formed sheet of filter material, like a thin furnace filter material.

Gilly