Crank housing hose

Hello A8 community

This is my first contribution. The forum here is really great. Unfortunately, I have little to no idea from car technology, so I try to 'quietly ask' you.
In the winter of 2005 I finally got my long-awaited car dream in the form of the A8 4.2 quattro. According to vehicle data from the service plan, the delivery date was November 1995.
So far I had no bigger problems with my 8s, but always small pecks. For example, since I started using the brake discs, as well as the brake bellows from the Digit Power (Canton Aargau, CH) with (according to workshop specifications) original parts! the brakes squeak with warm engine, often accompanied by the flashing of the brake lining warning lamp. Before the Digit Power visit, I never had this problem. A control view from the official AMAG/Audi representation in Zuerich could find nothing negative.
But here the story goes on. Since I discovered a slight but constant loss of coolant some time ago, I brought the vehicle into the said AMAG/Audi Zuerich. There I was told that either the whole bottled product with a slurry for approx. CHF 2500 can be replaced or a coolant (some sealing mass) can be filled into the system for approx. CHF 150. However, the Audi dealer advised me of the sealing mass, with the not entirely convincing reason that the sealing mass could be transferred to other systems and thus motor damage could be carried out.
Now ask the experts: is that true???
Unfortunately, the sealing mass has brought little, as a slight loss of coolness can still be observed.

Furthermore, it has been found that the crankcase hose is torn, but according to the same seller, this does not cause any significant interference for functionality and robustness. I just wonder why Audi installs such a crankcase hose at all.
Here is another question: what is the use of the crankcase hose and should I look to have it replaced as quickly as possible?

Can someone please give me a REALLY! Indicate competent workshop in the Basel or Zurich area (or elsewhere in this area) that knows where to put my A8 hand?

I hope that I have not terrorized you with my questioning and that I will remain in anticipation of your answers with friendly greetings from northwestern Switzerland.

Roberto