Using a strong light and magnifying glass, look at the "sensor" (it's really the OLPF, but I'm fine calling it a sensor) and see whether or not you can see these spots on the sensor. I wonder if these aren't old oil spots that have dried and hardened to the point that a simple cleaning won't remove them? I've read where people had to resort to high grade isopropanol to dissolve the spots. That said, perhaps paying for a professional cleaning might be safer. They'll have a tough time charging you if they can't clean it as well as bear the liability if something goes wrong.