How did the dealership miss this code before handing the car back to you?
I will answer this portion. Chances are, there wasn't enough of an "issue" to set the code yet. These sensors are oil driven. My guess is, you just found out where some of your metal shavings went, if there were any. But I wouldn't be too concerned with metal shavings. All motors have shavings to an extent. If you have a 115k on it, I wouldn't worry too much.
And to make a statement about doing the timing chain....A timing chain here in Detroit $2500-$3000 on these cars at the dealership. If I do it, I can replace balancer chain, balancer sprockets, all guides, timing chain (basically a kit for balancer and timing), WP, and 4 new coils, about $500. A new long block LDK from ZZP with a turbo....$2499. Which way am I going if a dealer has to do the work???? Choice is simple if I don't do the timing chain myself...