Good Day.

My awesome Audi mechanic says there are 3 different o2 sensors I have to order. He says order Bosch, non-generic.
I called up Audi, they told me there are only 2 different o2 sensors.

My other mechanic friend looked on WorldPac, and they say only 2 different types.
They also looked at All Data, and they say 3 different types (078906265M, 078906265N, 078907265P).

I'm so confused!

Does anyone know FOR SURE?
Also, where can I get these Bosch o2 sensors cheap online?

Thanks a ton (as usual to all those who spend their time giving answers to people like me)
-Christian from Monterey,CA