I was changing the thermostat on my M276 as a Preventative maintenance and I noticed corrosion in the hole where the Oring goes into the head with the funny little plastic piece behind it (you know what I am talking about if you have done this).

I found a fair amount of corrosion on the oring sealing surface of the block which I cleaned up best I could. I was going to change the funny plastic piece behind it as it is a known failure point but with the corrosion, I am worried what I will find there given the multiple sealing surfaces. It is not leaking and does not show any obvious signs of problems. Should I just leave it alone?

Car is a 2013 W212 M276 with 120k miles.

Thanks

thermostat
Here is a picture of the thermostat surface and plastic piece (inside) I am talking about.