I would call Sig and talk to them - but in general, I think problems with Sig mags are rare ....
I have 3 226's ( in 9mm and .40 ) and have had none of the problems you describe / although my guns are about 3 yrs old / but all 3 ran flawlessly right out of the box.
My recoil spring guides are metal - but I don't know that a well made plastic one would be a problem. I'm kind of anti - poly anything / but its a sign of the times.
Glad to hear you like the gun / I would probably run 10 - 20 boxes thru it and see if that changes anything before I sent a gun back unless it gets worse.