Thanks, @sfbp. No, both devices do not even begin to read the discs. I forgot to mention that I do can spot the read laser when looking at the lenses in the dark. Unfortunately, I don't have good units to compare. I also have, of course, removed all grease and regressed everything in the beginning.
I have noticed that, when everything's fine, the device should apparently immediately spin up the disc, begin and complete focus search right away and then start reading the disc. The E3 doesn't do that. It spins the disc but then goes "click-clack" moving the lens up and down six times before it gives an "Error". I suspected focus issues, but it passes the focus servo test fine. It does hang on "EF balance", but I am unsure what could be done to clear that up. Of course I fiddled with the FCBIAS and EF BALANCE settings in service mode, but that didn't change anything.
Without knowing what precisely an optical block is supposed to do on startup and in what order I don't think this is fixable. Would get a new one in working order, but I would only want to do this if I knew this type of KMS isn't prone to frequent failure.