I second the suggestion from Donna to look at the floor. Water flows down so if it's leaking behind the liner it's going to get to the floor someplace.
I would start from outside looking up at the wood to look for evidence of water leaks
. Discolored wood or wood that sounds "soft" if thumped. Bear in mind trickle of water can flow laterally a long way along the edge looking to find a way out. I know this first hand.
Then look under those seats, the cabinets and closets with a good flashlight. Leaks
can be fixed, once you can find the darn things. Floors can be a pretty big job to patch if they are rotted by water leak.
Torsion axel has rubber bar inside hollow axel, tire is mounted on arm that twists against that rubber when tire moves up and down. Rubber gets worn out over time so trailer "settles" lower as the rubber lacks the tension to hold the camper up off of the tire.
You can (and people do) use the campers with the axel pretty worn out. Ok for short trips, good roads and modern campsites that are level and smooth. Being aware that without shock absorption
of good rubber the tires
will wear fast, trailer gets pounded harder by bumps, and your trailer rides low enough to scrape back or front end if you try to back or pull into a steep campsite. So you may get to use camper before replacing a worn axel but will need to replace it at some point.
It is a neat looking camper, and has a nice look to the inside and a somewhat unique exterior too. Hope it works out for you.