One of my fans was spinning slower, the driver side one, so I went on to replace it. This didn't fix my problem, but I couldn’t find anything online with pictures how to do it so I figured I can post my process and how I did it, hopefully it will help someone. My car is 96’ S600 but I believe it’s the same with any w140 or at least very similar.



First I remove plastic in front of the fans by removing 2 plastic clips:

Next I removed the bumper that is held in at 6 places. Not sure if I had to remove it but it helped me with extra space, especially for the bottom clips.

2 at the top are 13mm


Next two are below and behind the bumper. To access it I had to remove little bumper inserts on both sides. Both nuts are 13mm


Closer look at bottom nuts (13mm):


And last 2 that hold the bumper are behind the wheel well up front. They are 8mm bolts.

Passenger side:


Driver side:


Once the bumper was off I removed the radiator support that's held in by 4 x 10mm bolts (red) and 1 x T30 screw(blue).
After this I removed a plastic piece at the bottom of the radiator fans, not sure if I had to but I did. It was held by few plastic rivets. Mine was only held by 3 but once I took it off it looked like it was supposed to have more.
This is where this plastic piece is located, it attaches at the bottom of the plastic fan. I think I could have taken it out with the fan but mine was loose so I just did it now.


Here is where the rivets are:



After taking the rivets out the piece was off. You can see the wholes on it where the rivets go. I had only 3 but it looks like it was missing few more.




Next I removed this bracket that radiator support attaches to at the top. Its just one 10mm bolt.



Next I unplugged radiator fan wiring on both sides.


Next step was removing 7x 8mm bolts holding the fan assembly.


Closer look at the blots behind the fan blades.




After these 7 screws were taken out, radiator fans were held only by 3 really strong metal clips (just a U-shaped metal) at the very bottom. I was lucky that mine was held by only 1 so it was easy to release it. To release I separated it with a big screwdriver. This is where having the bumper off came in handy I think. I had a lot of space.



Once clips are released radiator fan assembly can come out...


This is the assembly out of the car. Only thing to worry about are below 2 points with the red arrow. I was able to push the radiator toward the engine and clear the space for it to be lifted up.


With the assembly out, to replace the fan, I took out 3 x 10mm nuts (red) and pulled out the wiring (blue). Installed the replacement one and that was it. I just put back everything in the reverse order.