Acetone or lacquer thinner should make quick work of it. Actually unless you're running into problems getting the brake lever clamps on, then you could just clean and polish the center? For polishing the center, any decent aluminum polish will shine them close to chrome. For an added shine, hit the bars with some ultra fine sandpaper, like 1500 grit. The polish will take out the scratches, and it will remove oxidation and smooth the surface before polishing. Some bars have that sleeved style center, I usually just clean those the best I can, and leave it alone. No real way to duplicate that type of finish.,,,,BD