Purity: Uncertainty Regarding Semen Characteristics
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 346:
If some fluid is discharged by a man who is not sick and that fluid has one of the three characteristics mentioned in the previous ruling, but the man does not know whether it had any of the other characteristics, he is not considered junub and performing ghusl is not obligatory for him.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)