I would check the torque value on the new ones after reading of loose plugs on the Jazz. Sometimes needing a thread insert. I was lucky to buy NGK DIFR6D13 in Australia in January, for £40 for 4, from a national chain equivalent to Halfrauds. The factory manual states 18 Nm. But checked the NGK UK website, and it states 20 to 25 Nm with a DRY thread for that plug. But then, most just wang them up tight. I can't see dealers using a torque wrench either...