Congrats on you new (to you) trailer!
As said, if you find the holes in the roof a little Eternabond tape (and a LOT of rollering down) will seal it up permanently. Make sure to clean off ALL dirt and grime and then wipe it with acetone.
Toughest part will be finding the leak, because on aluminum the water can travel quite a distance underneath. Additionally, condensation on the inside might appear to be a leak from the outside.
IMO aluminum roofs are FAR superior to any other roof out there, and do not wear out unless they take a hit with a sharp object. The exception would be a two-piece roof with a seam in it. In that case the entire seam will need to be carefully covered with Eternabond.
Good luck!