Advice Needed

Hi everyone! I bought a 2015 428i with Xdrive about 8 months ago and I was hoping I could get some advice from you all.

A couple months ago I was taking a trip up the coast when I noticed smoke entering from the AC vents in the car. The heat was on so I figured this was smoke being diverted from the engine into the cabin. It had the faint smell of oil and rubber. I pulled over immediately and checked under the hood. It looked like the serpentine belt was melting, but there was also residue of oil everywhere. I checked the usual suspects (oil cooler, oil filter housing) and didn’t see any oil leaking from these locations. It occurred to me that this was probably due to the valve cover gasket seeping hot oil onto the belt and melting it causing the burning oil and rubber smell.

I was in the middle of nowhere and I was not going to drive it anymore so i had it towed to a shop. They said they looked for any signs of oil leaks but didn’t find any, and it was probably caused from someone doing a messy oil change. I was extremely skeptical and asked about the valve cover gasket and the ofhg, to which they responded drive it for a couple weeks and bring it back and we’ll check again.

This brings me to last night. Roughly 3 weeks after that mechanic shop diagnosis I once again smelled the burning rubber/oil smell. I checked under the hood and once again I saw no active indications of oil leaks, and the belt was still in good condition. However, on the right side of the engine (where the oil filter and oil cooler are) I noticed a layer of grime. It seemed like there was hot oil that may have been denaturing some of the rubber hoses and plastics.

I am wondering if there was more of a surefire way to confirm my suspicions of the valve cover gasket, or if anyone has experienced anything like this before. The smoke/smell only seem to appear on longer drives <30min. Any tips or advice would be appreciated!