Catalyst problems / screwdriver support

Hello to each other.

I'm new to the forum and have been driving since c. 1.5 years an A8L, 6.0 from 2001, which has now already run 243,000 km. Unfortunately, I'm layman and the salesman pulled me over the table as far as the technical side is concerned. I have already left more than 5,000 € in contract workshops since the purchase (motor electronics, wiper motor exchange, spring exchange, power steering exchange, water input right and left front etc.). Now the catalyst on the left seems to have given up the mind. The contract workshop wants to try to solve that problem with an "update". The odds are to be 50-50. If the cat remains defective, an exchange with indicated previous engine expansion is necessary. Now that my gold donkey has retired, I would be grateful if I could give you an assessment of my problem and, if necessary, of yours. the info about experts near Oberndorf a.N. The Commission's
If the list of defects goes on like this, I'm probably going to have to sell the car, which I want to avoid under all circumstances.

See you soon

hansjo