This is in a 1993 W124 300D.
I was supposed to use 85W/90 or SAE 90 according to the manuals but I couldn't find any at the parts stores.
I was actually only looking for 85W/90 and didn't know that I could use SAE 90.
The Castrol is synthetic but I definitely noticed that it was much lighter in color and thinner than what came out.
On my test drive it seemed like the whining I had attributed to the tires had diminished significantly.
I also filled the diff with the car jacked/ramped on the driver side so I probably got a little bit more in there than if it were level.
According to the manual it takes 1.3 liters but adding up what I put in based on the measurements on the side of the bottles I put in about 1.442 give or take a drop....
I also serendipitously learned that the boot for my driver side axle that connects to the diff is torn.
Have I jeopardized my diff with this weight oil?
How big a deal is my boot being torn?
I glanced inside the boot and it looked like the axle was coated in a whitish grease and I didn't see any rust or anything.
However, since the previous owner worked cattle in this car and I have found about a hundred pounds of sandy mud caked in various parts of the car I suspect that there has to be some abrasive material in the boot and on the axle shaft.