The surest way to find a leak is to take it to an RV service center and have it pressure tested- $200 or $300, I believe.
Or you can climb up on top of the roof again. Most leaks are at places where 2 different materials join. Look carefully at:
around vents, opening and protuberances. Look for cracks, holes, lifting edges, uncovered screws or missing screws. Check antenna boots and vent boots, if you have them.
Sides, edges and front and back caps. Again, cracks, holes, screws. Also look just over the edge of the roof.
seams on flat spaces.
The air conditioner (this may be hardest). There is a 14x14 1" foam gasket that seals the AC to its 14x14 hole in the roof. If that gasket gets old and too compressed, it doesn't seal anymore. You can see if this is so by removing the plastic shroud (4 or 6 screws) on the air conditioner and trying to lift or rock the AC back and forth ( its heavy!). Any movement indicates its loose on the gasket.
Good luck! Roof leaks are usually fixable by the RV owner with a little care and patience (plus money
).