I'm putting the engine of my '72 CB500/4 back together, and it's going well, but in the pack of new oil seals I got there is this little one that I did not see taking the engine apart - Mystery Solved: Turns out it's for the tachometer seal on the top of the engine...Mr. Moderator, you can nuke this topic if you want; I was so focused on the forest for the trees that I didn't even think about the top of the engine.
