Does the car shift hard?
If so, that can be the source of differential wear. I dredged up one of my old posts where I went through the same thing you seem to be going through now.
Excessive W123 Differential Wear - Pictures
You need to get that back cover off and do an inspection. And if the car shifts hard, take care of that also. In addition to doing an inspection, taking off the back cover will let you clean out the other accumulated metal shavings.
In my case, I cleaned everything out, filled back with Mobile 1 synthetic gear oil, and continued to drive for at least a year. It was certainly taking a risk, because at any point that differential could have come apart further and jammed - causing any number of a range of consequences up to and including loss of life.
Now I have a replacement differential in the car that is tight, have the transmission shifting gently, and expect the setup to outlast the rest of the car.
Hope this helps.
Ken 300D