From the look of the picture.......I would say that it probably wasn't parkerized in the first place. Parkerizing won't 'peel' or 'chip' off. Looks more like is was painted and the paint is peeling off. I don't own an SPS so I don't know for sure if that piece is steel or if it's just pot metal. Hell, it could even be aluminum.
I say do what sunray suggested and double check it with a magnet, if it doesn't stick, it's not steel and can't be parkerized. If it's aluminum you could paint it or anodize it (or both). And if it's pot metal or plastic, you have to paint it.
Make sure that if it isn't steel and you chose to paint it, to use the proper primer (for whatever material it is) so that the paint adheres properly and you don't have the same problem you have now.