And because that guide rib is heavily corroded, it is hardly possible to adjust it properly.
The points of the adjustment screws must be placed properly into the guide rib; usually, there is a clear locating hole where the screw is adjusted.

These holes are barely there anymore; it looks like a non-original guide rib, and I have decided to buy a new piece of bronze and make a new one out of it. Sanding won't do the trick anymore; the photo clearly shows that.