Cab over's on any RV where rain pressure is present and seal maintenance is lacking will be the first point of delam. Yours is a classic example.
You might not see anything inside but use an IR thermometer on the suspected area from inside and record the temp and then shoot a non impacted area and record again. I think you'll find that things behind the wallboard aren't kosher.
It is probably fixable but at what cost is a crapshoot. I'd low ball the price or look elsewhere.
Might be a cheap silk purse or an expensive sow's ear.