Is it valid to purify oneself from prostatic fluid (madhy) by washing the penis and its surroundings, and does dedicating ablution (wudu') for prayer invalidate the purification from prostatic fluid?

"Madhy" (pre-seminal fluid) is impure and invalidates ablution (wudu'). It is sufficient to wash only the affected area, without the need to wash the entire penis or testicles. The proof for this is what was narrated by Sahl ibn Hunaif and Ali ibn Abi Talib, may Allah be pleased with them both, from the Prophet, peace and blessings be upon him: "From that, only ablution suffices you," and "Ablution is required for madhy." As for washing the penis mentioned in some hadiths, it is either for recommendation or it refers to the area where the madhy is present. The purification from madhy is easier than imagined, and there is no specific ablution prescribed for it; merely intending to remove the impurity or to perform prayer is sufficient. It is advisable to ignore obsessive thoughts and doubts.