You ever try something twice, and do worse the second time? That’s where I’m at with Puzzle 43: I don’t remember what I did the first time, but I don’t recall it requiring so many parts! 
But you know what they say: if it works, it’s good code! 
My solution is based on the no-latch version of the Puzzle 34 solution. Despite the high part count, or maybe because of it, the logic is straightforward:
- The first blue ball will invert the left gear bit, then trigger a red ball.
- If the left and right gear bits are now in opposite positions, the red ball will be intercepted.
- Otherwise, the red ball will trigger a blue ball, which will be intercepted.
And now I’m off to study the book solution!