What is the ruling regarding someone who finds transparent, brownish stains from the effect of excrement on his clothes in every prayer or every two prayers, and is this considered سلس ( سلس البول - urinary incontinence or سلس الغائط - fecal incontinence) or is there another reason for it?

One must purify themselves from impurities and perform ablution before prayer if they are certain that what has exited is impure. If a person is afflicted with incontinence – which is the continuous flow of discharge such that they do not find time for purification and prayer – then they must clean the affected area, wear a protective pad, and perform ablution after the prayer time has begun. What exits thereafter will not harm them, and they may pray the current obligatory prayer and any subsequent supererogatory prayers with this ablution.