Help me identify this part on a rear diff (W124). Is it necessary?
 

TL;DR: What is this thick double layer thrust washer between the pinion bearing and driveshaft flange? Why does it appear so thick compared to part in FSM? Can I safely omit it?

I'm working on upgrading the rear subframe and axle on my 1991 300D with a diff from a 1994 E320 and a V8 subframe. I went to replace the pinion seal. People here have warned against replacing that seal unless it's leaking due to the crazy specific process to ensure proper bearing preloading. You've got to mark the nut before removing and reinstalling exactly as before.. Well, I ended up over tightening it and had to replace the crush sleeve that goes between the inner and outer pinion bearings (used to maintain preload on the bearings).

When I went to assemble the new crush sleeve with the little friction washers, I also inadvertently installed this thrust washer (see attached pictures) between the bearings where it wasn't supposed to go. I went to press the bearing onto the pinion shaft using a shop press and it was very difficult and I knew something was wrong - I took it all back apart then realized my mistake. The thrust washer didn't belong there and it got all deformed (along w/ my brand new crush sleeve).
It appears it belongs between the outside of the pinion bearing and the driveshaft flange. So now I'm thinking I need to replace the thrust washer.

However, I've heard that the thrust washer isn't present on some vehicles from the factory. Mine doesn't even look like the ones I see in diagrams (part # 1263530762 - it doesn't have the little tabs that click into the bearing). Also, I notice that this part is apparently no longer available (NLA).

Is anyone here familiar with this part? Am I safe to skip installing it? It seems to only protect the outer bearing from the force of the nut while tightening, is my guess.

(see # 143 in 2nd to last / last image - is this the same part?)

Differentials are Mad critical stacks of majic...

If it was there, it is required, and the crush washer needs to be set exactly correctly.

Skill and experience is REQUIRED with a diff.

Zero room for any changes or imprecise assembly.

You are going to need to exactly replace it.

Or get a replacement diff...