Update-Samsung shamelessly accepts the fault and tells that its a common issue with all Grands,S3's,S4's and other Galaxy's with same finish and mine is not a one off case.The solution provided is:-
1.Either keep buying that cover every 6 months,whenever the issue occurs,for 500 bucks.
2.Or give Samsung a legal notice regarding the matter...

Imagine,this is an advice provided by SamSung Customer Care..
BTW,have a look:-
White Samsung Galaxy S III having build quality issues too?