Is ghusl required upon the emission of madhiy or maniy due to dreams or talking about sexual matters, given the presence of a congenital obstruction in the sperm ducts?

If you are certain that what came out is madhi (pre-seminal fluid), then ghusl (ritual bath) is not required; rather, it suffices to wash the male organ and perform wudu (ablution) for prayer. However, if you are in doubt, then ghusl is required to remove the doubt.