Locating the leak source is difficult, but must be done successfully or any repairs are wasted money. I think the best leak detection method is
http://www.rvleaks.com/ , it costs over $100, but well worth the expense IMO. I agree, removing ceiling panels and drying out any water soaked areas are a must. To leave it alone means mold and mildew problems are a reality.
If you know where leak sources are, Eternabond is the best remedy for flat surfaces, Dicor sealant is best for abuting surfaces or corners, they make both self-leveling and vertical application types to suit your need.