I have been a very careful and proud owner of my 11inch 2011 MBA but today while cleaning my screen I noticed a horizontal mark that I cannot clean off with my cleaning cloth. I have tried wetting the cloth and wiping but still it does not come off I think its maybe the space bar that has imprinted onto the screen. I feel totally pissed with this as my MBA has been my baby. Is there any cleaning polishes that anyone could recommend? Please advise.