New engine for RS6 2018 with only 15k km

[RS6RK]

Hi,

My friend is looking to buy a RS6 from 2018 performance with only 15k true kilometers and always serviced by Audi. Currently the car is being sold by an official Audi dealer in Germany, but they have also indicated that they will be putting in a new engine as the old engine made a strange (diesel like) sound. Obviously nice to get a new engine, but also relatively strange with such low mileage, so three questions:

1) Happy to hear if somebody has seen this (bad luck) before or that this can only be realised with abuse (cold launch controls, etc.)

2) Would you have trust in the Audi dealer to do a proper rebuild or is this the start of more issues? I can imagine that the factory with their machines will always be better capable in building the car up properly.

3) Price is relatively attractive for the mileage and options; would you buy or walk away? I assume it "depends", but unfortunately I dont have more info myself. Audi is willing to give another year full warranty on the car