Is a small amount of madhy (pre-seminal fluid) that exits due to observing something lust-inducing excused, or is it required that its exit be without intentional arousal?

The basic ruling for pre-seminal fluid (madhy) is that it is impure. A small amount of it is excused due to the hardship involved. However, if lust is intentionally aroused and a small amount of madhy results, then it appears that it is not excused. This is because intentionally arousing lust is a sin, and the alleviation granted by excusing it is not appropriate for someone who intentionally committed a sin. Furthermore, the excuse is granted out of need, and there is no need to intentionally get soiled with impurity.