OK replacing O rings is what people call rebuilding. Its ... OK replacing O rings ... I dont see what is "re - building" in that.
And you do that if and only if the thing is leaking ... cos all O rings do is keep gas in or keep air out. 1 O ring keeps floats on when the bowls are off on 89-00 carbs. But they all keep air out (and if that is not working, the WD40 test will tell you) or it keeps gas in and that is evidenced by ... a river down your driveway ... Else rebuilding is useless. Figure out and fix the problem, it will be cheaper and more effective ... cos otherwise - after rebuilding problem will still be there.
Cool.
buddha.