eye- it's quite possible the leak is further up, like one (or more) of the marker lights. They are notorious for leaking. The water could then run down inside the paneling until it hit the window frame, then come in and make it look like the window was leaking.
Check the marker lights well.
I think $3k for something with that kind of water damage is far too much, personally. If the thing was perfect, inside and out, it might be worth the $3k. As an aside, boat racing friends of ours had a Honey for a little while that 'was the worst motorhome they've ever owned, apart from the Dodge 440 and 727" (they've owned something over 10 motorhomes since the early '70s).
