Going to do spark plugs on a customer's 05 CTS this Saturday. Side job at my house. I went to the dealer on Friday to grab the plugs and the plenum gasket and the parts guy said there was 2 different plugs available. I gave him the VIN and he still couldn't determine which plugs were it. He had 15 of one in stock and had 1 of the other, so I bought 6 and kept my fingers crossed. Any of you guys who have done this job buy dealer plugs and if so, determine which ones were correct. Don't want to get her car apart and not have the right parts to finish. I suppose I could hit another dealer but figured I ask here first.