When I installed my Rebuilt Rear Axles I missplaced the new Bolts and such that your are speaking of that came with the Axles.
I just reused my old ones with Loctite on the bolt threads and that was about 2-1/2 years ago with no issues. (And, after the job was done of course I found those bolt kits.)

The good thing is they are easy to get at so you do not have to hold up your job and if you want you can replace them later.

I do not remember what type of sealant I used when I put the Differential Cover back on but I know for sure I did not put it on Dry. I do not want to do any job more than ounce.

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84 300D, 82 Volvo 244Gl Diesel