I think you're right about the lens not being original - I finally managed to get some images out of the core, by unscrewing the lens entirely and holding it in from of the sensor by hand. It focuses about half an inch away, well beyond where the intended threads stop. However, it's as if I'm looking at a clear image through a mesh screen - there is a stationary, grainy texture covering everything. The edges of the image are darker too. Moreover, the shutter has yet to move except on startup, and after prolonged use the center of the image becomes "whited-out". I'm sure much of the image quality issues are due to the my janky connection to a TV, upscaling, and the fact that I'm holding (not very steadily) the lens. The focus issue can be fixed with an adapter, but the grainy images and progressive white-out are a little much to stomach.
The seller mentioned that he could not test the core, and that it might have damage. He did not specify any more than that, and failed to mention the obvious damage the she shutter, etc. I guess that's what I get for buying a cheap, used camera though. It looks like it has had a rough history for sure.
I do hope that it hasn't lost vacuum, that would be very bad. I'm unclear if the dead pixels are an artifact or not however. An awful self-portrait is attached.