The right size black gasket. Unscrew and put on the gasket. It's best to unscrew this system, take it to the store, the seller will match and sell the appropriate gasket and assembly at home.
None of these things, just replace the gasket with a new one. The old one must be rough and that is why it is leaking. Open the siphon and see how it looks.
The seal, however, was it. It turned out after cutting that one seal is missing. That's why it's liquid ... I didn't think that a "specialist" did it so that he forgot about the seals.