


Question about changing spark plugs on S240
I just bought 2011 S240 and I'm changing the spark plugs for the first time.
One side was normal: I pulled off the rubber spark plug boot and removed the plug with a socket.
On the other side (the oil-filter side), there was an additional rubber piece around the spark plug. I don't think it was underneath the regular boot, since it doesn't seem like it would fit inside it. It was actually blocking my spark plug socket from fitting over the plug. I had to pull off the regular boot, remove this extra rubber piece, and then remove the spark plug.
What is this extra rubber piece? Is it supposed to be there, and do I need to put it back? There was not such thing on the opposite side