The driver's door lock has never worked since I bought the car. The key will just spin. I took the handle out of the door but I can't see a retaining clip or pin anywhere to remove the lock cylinder. If anyone could tell me how to take it apart or link me a DIY, I will be very grateful!

This is what my door handle/lock assembly looks like:

 

I spent hours on this exact same project (new door) and ended up breaking it off because I got so pissed that Audi would complicate something so simple, so badly. Terribly shitty design. Sorry I can't help, but I definitely feel your pain!

 

just do the rear door handle mod so that no one can steal your car trust me its worth it, three attempts to take my car taught me my lesson

 

Yeah, but a thief can still unlock it from the trunk if they're smart enough to know about it.