Funny story...
The first time I disassembled a slip joint I didn't know the seal was there. I just pulled the 2 apart by the hardest. When it came time to put it back together, the old seal had perfect teeth cut into it, and I thought that is how it was supposed to look. I even spent a couple hours in CAD programming to cut a new cork seal with the same perfect teeth marks. Of course I later found out that the seal only had the teeth because I screwed up removing the yoke!! It only takes 2 minutes to program the cutter for a round seal, LOL.