Brew group cracks after cleaning

Have a nice day,

after the mold grew in the Melitta Purista from the circle of relatives, I have disassembled the coffee machine and brew group into the individual parts and completely cleaned.
After reassembly, the coffee flows down again as before, only the brew group cracks during pressure buildup, just before the hot water is pressed through.


I have not yet replaced the seals of the connection pieces and the piston, but greased them with silicone grease after cleaning - meanwhile, the machine has been in operation for 20 months and should actually have waited a bit longer.

The assembly of the machine and brew group went smoothly. After assembly, I additionally cleaned the brew group with a cleaning tablet and cleaning program.

In the gearbox nothing cracks and when turning and pushing the moving parts, including compressing the coffee powder. Only when the pressure is built up, the brew group starts to crack and if you look sideways at the brew group, it seems as if this is pushed out or turned out a bit and it cracks.
The brew group does not crack during press-through, but it does when the pressure is released, when the mechanical tension is released again.
When ejecting and going back to the starting position, you also hear nothing unusual.
The stop onNow

I thought that the hold-down moves minimally during pressure build-up and have here subsequently again the contact surfaces between hold-down and brew group housing minimally greased, in which I drove with the remaining grease on the finger over the contact surfaces

.



The brew group is tightly screwed, but easy to insert and remove. The stop (see photo) is also firmly clipped on.



Krachen tuts still, I am at my wit's end.
Has anyone of you had a similar and can already fix?

Here is a video of the crashing brew group