Is what comes out of a person afflicted with OCD—due to his belief that the place of urine exit is attached to his clothes, or due to obsessive thoughts during Wudu and prayer—considered Mathy that necessitates purification, and can it be treated as سلس ( سلس البول )?

You are not required to purify yourself or perform ablution merely due to doubt about the exit of pre-seminal fluid (madhy), because the default is that it has not exited. If you are certain that madhy has exited due to the thoughts mentioned, and you are unable to prevent it by ignoring it or delaying the prayer, then you must perform ablution after the prayer time begins. What exits from you during ablution or prayer will not harm you, as it is considered similar to incontinence (sals).