'97 E420 O2 sensor question.
 

My grandma's E420 has a code being thrown saying that the O2 sensor is bad. It says it's one of the front ones. Now, would I be wise to change both of them, and there is a claim that the left and right ones are different. What is the difference?
Also I have not climbed under the car. Do the sensors plug in on the outside or on the inside of the cabin?? The WIS wasn't clear on this regard. Where is this plug, and is there a special tool to get the O2 sensor out of the pipe.... or do I need to take the pipe off to get it undone??

Most likely the only difference in the front sensors is the length of the wires.

Low mileage car?? why replace good working parts? 4 sensors total.

In Canada the sensor may be more difficult to break loose.

Car is around 200K miles. I have no record of them being replaced yet....

Bosch suggests that normal sensor life should be 100K-125K miles.

Is the connector plugs on the inside or on the outside of the cabin of the car?? The pic in WIS was unclear as to the location...
Thank you for your time.