They've actually recently caught major retailers here doing that, dcshooter. It's technically illegal, if I recall correctly.
To add context to the K-5 though, mine wasn't shrink wrapped, and I don't think they usually are? So how would you know for sure?
Edit: Originally posted by JimDickinson I think you are right about the serial number range for the stains. Mine is a 417xxxx and its sensor is fine.
Originally posted by felixkh I believe K5s manufactured in 2011 should be free of the stains. These were an issue when the K5s were first sold in 2010.
Thanks for the confirmation guys.