are 100k mile wear items much like spark plugs,I changed plugs on a w210 at our plug seminar that raymond and a few other members attended and the plugs had not been changed in over 125k miles,he had no cel either and really did not notice anything ,he sure did note the improvement in mpg when changed.
Same with o2 sensors,by the time they have degraded enough to trip a check engine light you have lost several miles per gallon and potentially by running to rich an air /fuel ratio A/F risk damage or failure to a good set of Cats.
Any good indie can change them,any good guy with tools can change them, any good mechanic of which service advisor's are not
,can change them.
Heck even with some basic splicing skills,Greg with his already admitted all thumbs
can change them.
Figure out what 2-3 mpg over the next 50k miles adds up to,then add in the potential cats issue at CA approved cat prices and do the math
The op's problem was already solved by Moi over on mbworld.org w210 section,I figured that since the m119 is so prone to water related issues in the plug connectors that maybe he had recently washed his engine or ran through a big puddle.Turns out they had just had a massive rain storm and he had in fact driven through a huge puddle the same day the cel tripped for p0300 code.Dried it off no more codes
change your o2 sensors ,so I don't have to solve your misfire codes and cat failures