I'm thinking about purchasing a 1997 Rexhall Aerbus XL 3500 from a private party. The seller reports that he recently discovered a leak around the bedroom A/C unit, and that he had the roof sealed. ...
The leak may very well be due to the A/C anchor screws being loose which allows it to leak under the seal. Take the inside shroud off, find 4 screws, one at each corner, you will likely find that one or more of them are loose. If so tighten them snug enough to slightly compress the seal. This could fix the leak, however, if they are loose and tightening them doesn't fix the leak it may need a new seal.