We need more details. Does it leak when trying to hold pressure? When there's no pressure and just water in the reservoir? Does it leak when pumping? Is the Ooze portion leaking, or the water? (Sounds like water.)
To answer the questions: No, the blaster has to be taken apart. I've not been able to do this myself due to the difficulty in taking the Ooze pump handle apart. I'll have to sit down and figure it out again later, ask someone who's taken it apart, or use some brute force. I haven't had time to bother with the Oozinator due to other projects though; sorry.