When I pulled mine I assumed the bur was from the wear due to the heat and pressures involved. I am guessing that after years and years of use the holes in the Prechamber Nose get enlarged some.

I have never read of any sort of reamer used to clean the Holes at the Nose of the Prechamber.

I had not read this either but one of our Members on another Forum said that after surfacing the Cylinder Head the Prechambers may need thicker Seals/Spacers. If the Thicker Seals/Spacers are used a Glow Plug Reamer (normally used to ream out the Carbon in the Glow Plug hole) should be used to possibly ream off and metal on the not repositioned Prechamber so the Glow Plugs will fit properly.
But, I had not read that myself.

The Sealing Rings are Aluminum. A Propane Torch ought to have enough heat to expand them; the heat will not hurt the Prechamber.
I don't recall having that problem with mine.

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84 300D, 82 Volvo 244Gl Diesel