Someday

I began experiencing rough idle issues and it took about two days to throw a code. DTC showed misfire on cylinder 1. I Swapped coils from cylinders 1 and 3 and cleared the code to diagnose if the coil was the issue. Took about 24 hours and threw the same code misfire on cylinder 1. I swapped the plug wires 1 to 3 again and put a new plug in cylinder 1. After the new plug idle is back to normal and not rough any longer. Bigger issue is when I pulled plug 1 out there is oil on the plug threads. I pulled plug 3 to compare and it is dry as a bone. I’m certainly concerned about the oil on the plug. Is the oil something I should be concerned with. I am very suspect given that the misfire was on cylinder 1, and that plug is fouled with oil. Looking for advice... Truck is a 2012 GMC Sierra with 5.3L vortec with 67,000 miles. I’ve attached a pic of plug 1.