My wife's car is a 2018 Mercedes Benz GLC 300 with the 2L turbo engine. The car requires spark plug replacement at 30K miles. Seems a bit soon with the current generation of iridium spark plugs but that is a different issue. Feeling fairly mechanically inclined, I was prepared to do this myself. I have changed hundreds of spark plugs over the years. Some more challenging than others. The access does not seem too bad in this engine. I noticed NGK, Denso and Bosch do not list a replacement plug. I thought this was a bit odd. Did some research and found out several things. First, only MB manufactures a plug for this engine. (please correct me if I am wrong). The second, and more troubling, is that these plugs MUST be indexed so the open area between the center electrode and ground wire faces the injector or the engine can fail! A MB service bulletin shows a properly indexed MB plug compared to an improperly indexed NGK plug which resulted in a piston crown melting with catastrophic engine damage that, of course, was not covered under warrantee. The technique calls for the correct MB plug torqued very carefully to spec which should result in the plug being properly indexed. First question, has anyone heard of this being a requirement for any passenger car engines? I have known about indexing plugs with race engines. Second, how accurate a torque wrench would someone need to be sure to accomplish this task? I am not sure of the accuracy and precision of consumer grade torque wrenches and how often they would need to be calibrated to ensure success. Could carbon or any other contaminant on the threads of the head give false torque readings which would result in failure? The procedure makes it sound like a crap shoot unless you bring it to the dealer. If they screw up, at least your engine is replaced in warrantee.