It appears not to be a Selenium cell John, although at first glance you'd think it is. I'm well aware what Selenium cells are, how they work etc, I've been using them for around 55 years
The camera came from a FADU member, it's an odd one not in the English language manuals or other publications, with this meter. There were variations not listed, after all early models had Compur shutters, then various Eastern German shutters. It needs photographs and comments on what affects the meter, it's not the front "cell", rather an opaque window 90º above it. Believe me it's weird.
It's strange which Selenium meters fail over time, oddly it's some of the better ones, Weston Master V and Euromasters are the worst, and then I have a pre WWII Avo meter that's still accurate, also a pre-WWII Gossen meter that's similar still accurate. I know that the Olympus Trip cameras relied on their Selenium meters, and a fix is to move the position of the wires on the cell as it's not the cell itself that has deteriorated rather the connection. But hey I use much older cameras, mostly.
Ian