Does pre-seminal fluid (madhy) exiting inside the vaginal opening, without coming out of it, nullify ablution (wudu')? And is it permissible to place a string at the head of the vagina to prevent the exit of pre-seminal fluid for someone afflicted with madhy incontinence?

A person afflicted with سلس (urinary incontinence) must perform ablution (Wudu') after the time for prayer has begun. It is permissible for him to perform Wudu' for Friday prayer before the sun declines (Zawal) if he wishes to attend early. As for tying a string to prevent the discharge of prostatic fluid (Madhi), if it indeed prevents the Madhi from emerging, then the ablution is not invalidated by it, and there is no harm in it as long as it is not harmful. If the matter is merely a result of obsessive whisperings (Waswasah), then one must not pay attention to them.