if u see red areas i dont think u can regain the chrome shine at that spot back,,
u would have to rechrome..
other solution could be to cover with solution tape,, or paint it,,or install a foam tube sorta thgingy on it,,,
however let others reply here as i m also interested in tis question as my crankcase has some acid fallen on it and cant remove that,, used thiner on it,, both sides of crankcase have spots of acid,,