Nice! ... but ...
I'll share with you that often the hardest part of framing a puzzle is to cover all the contingencies without using a hundred sentences. The great puzzle maker Martin Gardner did it best; it was part of his genius, apart from the puzzles themselves. You touched a base that I didn't cover. Nice going. Now I'll cover it.
I hadn't thought of getting just one circle. It may be a philosophical issue whether a slice can ever become a line. But for the purposes of this puzzle, I'll define a slice as an operation that leaves portions of the object being sliced on both sides of the slicing plane. I don't mean to change the puzzle midstream, I just envisioned, but did not clarify, that a slice would divide the object into two parts, creating opposing faces, which if glued and then joined, would restore the object. I think that rules out getting just one circle; you'd always get two. Not two in the sense of the two opposing faces, two in the sense that you described.
And, if we're tracking progress, had one correct answer; now there are two. Huh?
Yep, two, and that's a clue.
As well as a rhyme.