Hi Hazeloop,
I am another long term SOTA owner. It looks to me that you have swirl marks on the dust cover. You can bring it back with a little elbow grease or a random orbital polisher if you have one. Go to Autogeeks and get the smallest bottle of Menzerna 2500. You can use a soft foam polishing pad on a random orbital polisher or a clean microfiber cloth and elbow grease. Rub vigorously in a straight line across the entire surface. Repeat until the marks are gone. After you bring it back clean only with a fresh microfiber cloth. Any dirt will scratch the cover. I spray with 50% isopropyl in distilled water. This will safely remove any fingerprints.