I just checked the Walther website and it looks like all of the support for the PPKS goes through someone in Arkansas now.
Here is the phone contact info : (479)242-8500, ext 7.
Here is the online form for customer support if you would rather contact them that way:
Customer Support - Walther Arms
I would be very surprised if they didn't fix this for you at little or no charge. It is not an unknown issue with these guns.