To isolate leaks you can try a water hose. Start at a little below where you see water coming in, and run water gently, and very, very slowly work your way up. Do it on one panel at a time. This can be a very long process, it can take several minutes for water to work its way thru. There is the possibility that you can make it leak somwhere that it wasn't leaking before, or that you miss the leak completely, because a hose isn't rain. Be careful. Wet metal is slicker than goose s**t.
DO NOT attempt to seal the seams with tar. Get your bucket of tar and throw it as far away down the alley as you can, along with any kind of roll over paint crap. (Assuming you have a screw down type roof, as opposed to standing seam.)
5-v crimp roof panels are designed with a channel in the seams to allow whatever water blows in between to run out at the bottom, so putting goop between or on seams usually only damns water up and causes a leak farther up. Anyway, caulk is much easier and cleaner. If you do seal a seam, you have to go all the way to the ridge to keep water out the whole way. Be sure to caulk in between the two panel edges, not just on top.
But before you do all that...get up there and inspect.
Most likely the screws or nails have worked loose. You can re-tighten, and/or seal with some good caulk (silver gutter seam sealer, not plain latex, not silicone, and definitely not NP1, ), and or remove the old screws and replace with slightly larger so that they tighten up.
Other likely leaky spots could be anything coming through the roof, vent pipes etc.