How to Replace Mercedes GLS450 Spark Plugs - This is a detailed video showing how to replace Mercedes GLS450 spark plugs, including how to remove all the pieces to actually get to the spark plugs. Toward the conclusion, there is an overview of the tools needs to do this job. I ordered my plugs from rockauto.com, as of this writing they are about $62.00 plus shipping. If you prefer Amazon, here is the affiliate link for the spark plugs https://amzn.to/3D0BZ66 About $84.00 with free shipping...so, similar bottom line.
Be sure you order plugs that are noted as "indexed" so that the electrode is oriented correctly in the combustion chamber.