Does ghusl guarantee the cessation of madhy (pre-seminal fluid) after janabah (state of major ritual impurity)? And what is the ruling on the prayer of one who finds traces of madhy after performing ghusl, both as an imam and as a follower?

If a person finds a trace in his underwear after sleeping, and if it is semen (maniyy), he must repeat the prayers he performed after his last sleep in those clothes and before performing ghusl (ritual bath). As for his prayer as an imam after performing ghusl, it is valid, as is the prayer of those behind him. It is apparent that what he found is not prostatic fluid (madhiy), because madhiy is thin and leaves no solid trace after drying.