Sorry for your woes. You might have your best luck checking with a local RV repair place for an evaluation of your problem. The rear window AC on a '97 may be a previous owners modification. I have a '96 16 foot Casita, similar to your Patriot in style and age and the AC is mounted in the lower closet area between the bathroom and entrance door. That is, I think, standard practice of that vintage on 13' and 16' rigs, and still used today.
A window mounted AC puts a lot of stress on its attachment points and sealing integrity as it overhangs so much with heavy components cantilevered away. Bouncing down the road is very rough and tough on anything attached that way. And you do bounce....an awful lot.
2 options come to mind: fix and reinforce what you have or move the AC location to the front of the trailer as is standard. Another suggestion is to place the AC in the window ONLY when you need it. A pain, but some gain.
The other caution is to be sure your water leakage is from the AC. I've had to reseal my roof top vent and side windows from rain water getting in through them. Old rig......equals repair/maintenance work.