Melitta Caffeo Bistro 960: Coffee runs in a bowl

Hello!

Now the machine is defective again. Last time it was the thing with the drip tray indicator, the trick with the replaced capacitor from the forum here has helped. But for a while now, first sometimes no or very little coffee came, and now none at all.
The steam thing still works. But the coffee ends up at the bottom of the tray, dripping out somewhere inside.

I removed the drain valve - no limescale, all clean, looks good.
The drain valve looked bad at first, a lot of coffee residue in the spring, but hardly any limescale. I cleaned it and it looks okay to me, reinstalled it can be pushed with reasonably little force. I can see though that the thing won't open when in use.

What could it be? Is the follower not packing somehow? Doesn't look like it could be slipping or edging. Motor too weak? I'm a little stumped right now.
The position of the driver is as described in the Coffeemakers.

After the last repair, I had gotten a defective machine on eBay, for spare parts. Just tried it for the first time - water gets hot, but nothing else happens. Let's see which is easier to fix, at least I can swap components back and forth. In any case, I'd rather have our own, it's comparatively clean.

And one thing is very clear: My wife needs her beloved machine quickly again.

I have now replaced the drain valve and coffee comes again. What exactly was broken - no idea. So right I still do not understand the machine, but it seems to me a miracle of Ingenierurskunst to be.

Do I now reassemble everything properly, or do I do that tomorrow when it comes back in new? To be on the safe side I had ordered the set with seals. Hmmmmm. First drink away the test coffee.