Are the tiny drops that are discharged after slight contractions pre-seminal fluid (madhy), seminal fluid (manyy), or merely natural moisture, and do they necessitate a full ghusl for janabah, especially given the suffering from obsessive-compulsive disorder?

The cure for obsessive thoughts is to ignore them. If you doubt that something has exited, do not pay attention to the doubt, nor investigate it. If you see something that could be either madhiy (pre-seminal fluid) or sweat, the default assumption is that madhiy has not exited. If you are certain that madhiy has exited, then wash the tip of the penis and perform wudu' only. Ghusl (definition) (ritual bath) is not required unless you are certain of the exit of maniy (seminal fluid) which necessitates it. Giving in to obsessive thoughts places a person in difficulty and hardship.