I need some help, i have an A6 2002 Quattro 6speed manual, 98,000 miles, and the dealership is telling me that both my catalytic converters are bad. They quoted me $3,200 to replace them.

The questions i have is, do these codes mean that my O2 sensors are bad or is the dealership telling me the truth?

The P0421 and P0431 are "Warm up catalyst bank 1 & 2 efficiency below threshold sporadic. Could this be the O2 sensors?

P1127 is long term trim mult. bank, system to rich.

I have a cold air intake (LLTEK), APR Chip and APR cat back exhaust.

Please help me understand if i am about to be screwed by the dealership. And also if anyone knows of any aftermarket Catalytic Converters for an 02 A6 Manual Quattro. All i can find are for Automatics?