Hi Garry, I can do a bit better now, as I have found the metal overflow tank that I had repaired and then painted. In the picture below, there are in fact four types of radiator overflow tanks. Obviously, the black one is the one that (I think) you are referring to.
That one , as it comes in two halves, has been pulled apart and re-soldered professionally. I had used it on Gleaming Beauty purely for curiosity value, but as it kept on seeping, I decided to replace it with the latest type plastic unit - that is the one with the strengthening ribs. When buying those, you will also need to purchase the plastic plug and circlip to close off the opening for the temperature control unit. That unit, incidentally, cannot be used on a 116 on account of the close proximity to the battery. Another so called drawback is the large outlet for the hose that leads to the bottom of the radiator - it is a very special hose with unequal sizes at either end and will set you back at least a hundred dollars (when I checked about four years ago).
There is also the earlier type plastic tank - the same as the black metal one, and with both you can use a far simpler hose, probably procurable from outside sources. So that can be an advantage. Last but not least, the bullet shaped overflow tank - made of brass and taken off a 1968 - 300SEL. I believe they have a similar, if not the same unit, on other Mercedes models as well. It is for sale, if anyone was interested for $60.00, as are the black metal one ($45.00) and the old style plastic unit for $25.00. Regards Styria
N.B. Apologies - for some reason, Photobucket is not allowing the transfer of the photo. Will have to sort that out. Photobucket working again.