In the event anyone's doing plugs anytime soon, I thought I'd let you know. It's a manufacturer's rebate and I've called Delco to confirm that ANY retailer's receipt is valid for the mail-in rebate. Find the form you need to fill out/send and instructions by Google-ing "2015 AC Delco plug rebate". Just about spent $9/plug on NGK's, now I'm getting Delcos for half the price after rebate. 
