hi mate,
is e e yellowish spots u r talking abt in lump form??? if it is, there is noting much u can do...........if it just some stain, u might want to try using a "Shiner".....tat is wat ur wife would use for shining her nails.......
it is a ice-cream stick looking shape with file on 1 side n shiner on e other side......tat should work on some stains but not sure it will work for ur case.....
Important: do not steal ur wife's shiner or u'll be in trouble.......
u can get it frm Guardian or Watsons........