Prima Donna avant, milk froth cover breaks off.

Hello
after our Prima Donna has so far worked without complaint for several years, now makes the milk foam problems.
After pressing the button, the machine starts to produce milk foam. After a short time, no more foam comes out of the tube. Only air comes out. Until now, it was possible to restart the frothing process by briefly interrupting the process. But that is now also no longer possible, comes almost only hot air.
It looks as if the milk is not sucked up to the top.
I have partially replaced the seals on the connection. I have cleaned the milk system regularly. Where is the error?

Too bad, there used to be more going on here!

Hi,

probably because you can only recommend the adapter on the machine to change and hope that it then goes again. I assume that the steam is sufficient.
These tips there are masses on the net.