Hmm thanks for the input! The bike isn't exposed to salt, I don't live near the sea and it's hard to imagine the previous owner sweating so much the entire handlebars start to turn white by the ammounts of salty sweat that gets poured over them!
Anyway I bought an aerosol can of auto wax today (much cheaper than I expected at only €2,-) which supposedly protects painted surfaces, copper, silver, chrome, marble, artificial leather, and plastics from UV rays and chemical influences. Let's hope it also works on aluminium and corrosion or oxidation can be considered a chemical influence
I'll keep you posted on whether it works, if it doesn't Pantene might be worth a shot.