My wife has a P238
I think Sig had some issue on the very early pistols produced.. My wife's is S/N XX71XX and has had NO issues with her pistol at all from the start.. She has a couple of hundred rounds through it at this point.
If your S/N is around hers or Higher, then I'd insist on Sig taking a look at it. (I'd probably insist regardless of the S/N).. Like you said, it's a $600 gun (my wife got hers for $450 BTW), If it has issues, they should correct any it!!!