I have a 1986 31' Sovereign
. Mine had leaks along the seams of the endcaps, but I later found out that they had been replaced & weren't sealed well. Chances are, yours will be original. I do have a hint for you, though. While going around the outside of the trailer, do some thumping on the lower end of the banana wrap (where the bend is on the bottom of the trailer by the belly pan). If there seems to be a lot of junk rattling around in there, it could be a problem. Mine had lots of rust from the outriggers & chunks of flooring (they used chip board in the mid 80's) that rotted & fell into the lower banana wrap.
I have addressed all the problems associated with the water (frame, floor, etc.) and have the trailer all spiffied up. It now is a beauty & we're going camping in it this week! I too love the floor plan & adore the oak cabinets. I had a '76 Overlander previously, but didn't care for the flimsy interior.
Try to look under the beds for any signs of leaks. At least that won't be covered by wood flooring.