Erm, yes, I indeed forgot to mention that I'd taken the trigger unit apart (the photo captions should make that clear though). I've left the trigger guard pins half unseated to facilitate the next disassembly.
There is no grease on the sear, nor any burrs, and backing of the adjustment screw no longer helps. It did for a short while, but the pistol just doesn't cock anymore. There are no usage marks whatsoever on the piston that could have been made by the sear - I'm guessing that the pistol shipped with a badly hardened or adjusted part (the sear barely protrudes into the cylinder). Replacing the part is simple and ought to take care of the issue.
mad(dened) scientist, fulltime nerd, (early) music/photography/Moto Guzzi geek, discovering the joys of shooting