Are prayers valid when madhy is discharged unintentionally or without lust, and one is unable to distinguish between maniy and madhy, and it is sufficient to wash the affected area and perform ablution for prayer?

Your prayers are valid, and you are not required to repeat them. Whoever finds something after waking up from sleep and doubts whether it is manī (sperm/seminal fluid) or madhī (pre-seminal fluid), has a choice: if he wishes, he can consider it manī and perform ghusl (ritual bath), or if he wishes, he can consider it madhī and suffice with wuḍūʾ (ablution) and washing what it touched.