Repair it and see how much space you loose. Worst part of it is you loose that much space now all all drives in the array.

Did you do a full (LONG) format when you remade your partition? If you just use quick format bad sectors get missed. Now I always do a full format (which takes like an hour for just 500GB) and I always see a shrinkage in size from the removal of the bad sectors.

If I was in your shoes I would redo ther raid low level format each drive and then rebuild the array and do a long format. I don't think you will have much luck getting a RMA unless you loose over 10% of your drive space as it would probably be within manufacture's specs which are probably listed somewhere in very tiny print.