The solution:
And the permalink:
https://www.lodev.org/jstumble/?board=rlerlf1fellfr1felrfrelflrfrelfrreei
In the one case where we need to send the blue ball right to hit the red lever, we know that the bits are afterwards in a position that leads to the interceptor. Hence, we can use the OR gate to replace the crossover and a whole bunch of ramps to get there.
I was trying to build a similar solution for Puzzle 19, but I’m not sure whether it’s fine if one or two additional red ball ends up in the tray at the bottom for some inputs?