According to the owners manual, spark plug replacement is at approximately 50K miles ( maybe I read it incorrectly). I called the dealership and the mechanic said 100K is suggested. When did you replace yours and what brand?

Is this operation easy to DIY or best to have the dealer do it?

 

Buy accessories from a Mb dealer, then you know they are right. I bought plugs from a place like autozone and found out they were not the right ones. Look at the thread about an oil filter ruining a motor, so many small parts to make a mistake that can really be serious. I have my Mb plugs but have not changed them yet, I think it's not an easy job. You probably will feel a performance boost at 50,000

 

I've changed the plugs on all my cars (domestic and foreign) over the years and have never bought plugs from the OEM. I just take an old plug with me down to my local auto parts store and match the numbers or I buy them online and have them shipped to my house. As long as you match the make and number of the plug, you will be fine. Also, it's not a hard job, just have to remove some items (air inlet, plug coils) to get to the plugs.

Also, I have never noticed a performance increase due to new plugs unless I've waited way too long and the car is running rough because the plug gap got too large on the old plugs.