Cleaning Glass Hard Water Etching

I've been cleaning my 110g tank since it's been stored in my basement since 2013 . I've got it all clean except for the center brace , I've used vinegar , Bar Keep ,scrub pad and wet-dry sandpaper and still can't get the etching off ? Any one come across this problem ? Will treating it like a scratch work ? So Sorry can I get this move to the right location ? Thanks