2010 S6 - Replacing Engine

Hey guys.

First post here, but long time lurker. I’ve had my S6 for a few months now and my shop is just getting to the bottom of my oil leaks. After engine out it seems the block had already once been machined and improper gaskets were used.

Unfortunately the shop says I have two options: enjoy a leaky car or replace the entire engine! I’ve invested too much into the car to sell it too.

Wondering where you guys would source an engine for the S6 from? Can I use the S8 motor of the same generation? Would you go used, new oem or perhaps one out of a wreck?

Thanks for your time! Any help or input is greatly appreciated as I’m really new to this stuff.