Please clarify. Is this on the wall of the RPod body between the roof and the top of the slide-out roof or on the wall of the slide-out between the flange and the window?t?

Unfortunately, there is likely no easy way to do this. The dealer is probably better equipped to do the work of finding the leak. One way that possible is to make a plug to fit tightly into an open window and cut a hole for a duct. Use a squirrel cage fan, much like the ones used to inflate the bouncy castles or slides. It would not need one that big or powerful, but you do need to be able to build some pressure. Once that is done, use a soap solution to go along the seams and spray them. Any leaks should be made evident by bubbles appearing where air is leaking. Once the leaks are found, then probably Dicor lap sealant after cleaning off the leaking area well with denatured alcohol.

I'm not sure what the "commercial grade tape" was that the previous owner used. That will likely need to be removed both to test, and to fix the leak. I've read good things about Eternabond. However, I would still lean toward self-leveling lap sealant if it is on a horizontal portion of the roof or non self-leveling if it is on the curved or vertical portion. If it is the slide-out roof that is the problem, then that does have Eternabond tape already. That would need to be removed, the area cleaned, and the tape replaced with new tape.

I'm not sure if this is the best answer, but it is the way I would proceed. When I worked for a boat-building company, we pressure tested the boats to find leaks before they were shipped to the new owners.