An 8 yr old rv is an 8 yr old rv. You could hire an expert to do an inspection for you. Probably a few hundred well spent.
At 8 yrs old it depends on how much time the previous owner put into maintaining it plus...did he know what he was doing and did he use the correct products ?
Keep in mind that water will seek the lowest point to settle or exit, however a leak in the front passenger side could travel and exit in the rear drivers side. It would depend on how it sits when parked most of the time. That happened to me.
Inside: Look for signs of leaks (water stains or re-painted areas) inside cabinets using a flashlight as well as your nose. Beware if an rv is all opened up to air out when you go to look at it . Most of the time a closed tight rv will have an odor from dampness or mold.
Exterior: Feel the exterior for soft spots by banging on the walls. If it has a rear ladder, check the mounts for dried caulk. Rear wall replacements are common enough to be a concern in any rv.
Climb onto the roof and inspect all the things that have caulk. Roof vents, vent pipes, antennas, all seams should be clean and smooth not dried and cracked etc.
Cabover leaks can occur because the top front cross seam takes the most abuse . Check windows and clearance lights also have tendencies to leak. Some people put a bead of caulk around the exterior gaskets of the windows as a precautionary measure as well as the glass in the entrance door which show signs of leaking at the bottom where the door meets the sill.
Check the floor for soft spots especially near the entrance . Sometimes a leaking door will seep under the floor entrance area.