Is ghusl obligatory when a clear, non-mani fluid is discharged from the penis upon thinking or talking about sex, or during defecation?

Talking about and thinking about sexual matters to arouse desire with someone other than one's wife is inherently forbidden, whether or not it leads to any discharge. However, with one's wife, there is no objection to it, though it is better to avoid it. What is discharged due to this is madhy (pre-seminal fluid), and it necessitates washing the entire male organ and invalidates ablution (wudu').