Engine Exhaust System problems of the 2001 Audi S4

There was a cam adjuster from where the oil leak was coming from. Noticed this on August 8, 2003. Then, on July 24, 2004 took the vehicle for an oil change a nd they confirmed there was another oil leak. The warranty expired in November 2005, and the consumer made arrangements for the gaskets to be replaced a month before the warranty ran out. In order to get to the gaskets the cam shafts had to be removed. The gaskets were replaced,, and cam shaft reinstalled, then gave it a tune up. Also, put in two different types of spark plugs; one set was platinum and conventional. A week later, it was ready for pick up. The exhaust sounded different when vehicle picked up. On January 31, 2005 took vehicle to another mechanic because the check engine was on. At that point mechanic determined O2 sensors caused the light to come on, and the exhaust sounded differently. Then, three months later, the exhaust cam shaft that broke it bent valves in cylinder head and caused it to crack.