rear end problem ?

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Unfortunately I couldn`t figure out what exact rear end this car has but I want to know.
I`ll be glad to get good advice from forumers here!

I decided to replace the rear axle fluid and chose to use Valvoline 75W90 fully synthetic gear oil. If this was a mistake then I will redo the project and flush it out.

The system uses 1.7qt of fluid (this is what a 740 gasoline old 1988 manual suggested for a 740 gas car but my car is a td, ... IDK) which I could only add all in by lifting the rear of the wagon up (tow hitch comes handy).

I had to use a torch and hammer to get both plugs out. This rear axle fluid job hasn`t been done for a long time.
At least I had about the same amount of fluid in there what is necessary though, I don`t think fluid was missing, or very minimal.
The old fluid looked very dark, dark green actually, it was/or looked thicker than the Valvoline I used to fill it up.
The drain plug had some fine metal paste on it. I did wonder how it looks inside but did not check because I had no new gasket for the cover. Next time...

I read that for certain types of rear axles special additives are suggested to be used but again I have no idea what this Volvo has.

PS. The Valvoline gear oil bottle said GL 5 on the rear label.