Audi Repair: Water in engine, electric switches, oxygen sensor

Question
Hi, I just had my Audi repaired after the timing belt jumped some teeth. On re-assembly water managed its way into the engine, mixed with the oil. The mechanic explained that it's related to the catalytic converter being faulty. He intends replacing certain parts, I only know that it's linked to 2 electric switches (one white, the other blue - at the back of the engine). He assured me that the engine is OK and no other problem exists. It just sounds strange to me and I could not find any way of identifying these two particular parts in the manual. Does this make any sense to you?

Answer
Hi
I think maybe  oxygen sensor's ?
If CAT or CATS goes bad it sets MIL ( or check engine light) light on and cats needs to be replace.
Light can be reset but it will come back ON. How the water got inside the engine?  that's what sound strange to me.
good luck