Is it obligatory to perform ablution and pray immediately upon being certain that intermittent madhiy has exited after performing ablution for the Fajr prayer?

The default is that madhy (pre-seminal fluid) does not exit until one is certain of its exit. It is obligatory to perform ablution (Wudu') for the Fajr prayer without waiting to ascertain its exit. If the madhy does not exit regularly, then the ruling for a person with سلس ( سلس البول - urinary incontinence, or سلس الريح - chronic flatulence, or سلس المذي - continuous flow of prostatic fluid or madhy) applies to you.