That is definitely the same thing. Do we know exactly where it goes or what purpose it serves. I don't suspect that it is a critical enough part to warrant tearing my pump apart to replace it. I'm just curious now.
Probably not worthwhile replacing. I couldn't even find the part for sale anywhere.
Perhaps, it would be worthwhile getting one and replacing it if you ever need to do a seal change.
Note that parts 3 and 4 are switched in the Pentair catalog. Part 3 in the picture is the v-ring. Part 4 is the capacitor.