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@biconvex: it is Nr. 016753. In fact the glass looks a bit dusty. If you have a more crisp version i should think about a cleaning of that lens, but i do not expect a strong improve since the lens looks quite OK to me.
There are two versions of this lens. The first one has the serial # on the front ring and a min aperture of f/22, the second one has the serial number at the bottom of the aperture ring and a min aperture of f/16 (There was also another version sold as 'Color Reflex MC' without the 'Porst' designation on the front ring, but this one seems to be the same as version two).
The Porst lens (made by Cosina, also sold as Cosinon 55/1.2 with a slightly differerent focus grip) was introduced at the end of the 70s, and since the version 2 has some similarities in appearance to the Cosina 55mm/1.2 (also sold als Revuenon, Ricoh and Vivitar 55/1.2 with slight changes in outer appearance; not the same lens as the Cosinon) that afaik was introduced in the beginning of the 90s, I suppose that version 2 is the younger one.
I have seen a lot of pictures from version 1 Porsts that show excessive glow wide open. I have never owned a version 1 so I was not able to make a direct comparsion until today but I have two version 2 lenses and I was never able to recreate that glow. In fact, my Porsts showed less glow wide open than the highly regarded Pentax SMC 50/1.2 and SMC-A 50/1.2 that I once tested them against (their border/corner performance was much worse though and they did not get as sharp as the Pentaxes stopped down).
From your serial #, I take it that yours is a version 1? I have only seen 0xxxxx serials on version 1 Porsts so far.