On my 1998 C230. because of draught restrictions hadn't cleaned my OEM wheels in some four or five months. I tried griot's garage hand polish, P21-all purpose metal polish, Oil Flo Desolve, P21 citric all purpose car cleaner, and made very little head way with all these products.
The product that finally worked, 3M brand MEDIUM CUT rubbing compound, (part # 39001), First cleaned wheels with Griot's Garage wheel cleaner, dried wheels, then with a 100% cotton terry towel used tons of labor intensive polishing with the 3M, and my wheels are smooth and gleaming, removed the small imbedded black particles. and the golden tar like finish that had marred my wheels due to lack of cleaning. From now on my car gets it's wheels washed once a week and waxd periodicly. Important thing is to clean and protect, and the products to be used are those that you would use on your paint.