Inside the wheel well looking at the engine, towards the front you'll see caked oil or "spillage". I guess it can happen on either side but most cases (including mine) are on the drive's side. It's easier to see from the wheel well or underneath but you can still sort of see the oil leaking/caked from the top of the front of the valve cover area if you look hard enough.
Here are some other people's pics from a quick search. If you have it I'd get it taken care of under warranty before the powertrain runs out. Otherwise you're looking at a $1800-$2000 job. My dealer quoted me 11.5 hrs. It's super common on the 5.7. I could easily do it myself but that's what a warranty is for. But they change the oil and coolant too so bonus free fluid change.
Edit: They can creep up anywhere from 10k miles up to 100k. No real rhyme or reason.