I am sorry you are having issues with your trailer. Window and roof leaks are something that any owner hope they never encounter and are very hard to diagnose at times.
As far as the warranty and being 5 months past the expiration and Keystone refusing to warrant it; in all honesty IMO opinion it is understandable. Like a vehicle someone buys with a 12mo. warranty and the tranny goes out 17 mos. later and they refuse to give them a new one for free (which they won't) it's just the luck of the draw for lack of a better term.
As far as a resolution for the leak, I hope the technician that inspected it and submitted it knew/saw the issue and knew what needed to be done. He should share that with you so that you can take whatever measures you think you need to. Far better than folks sitting out in "keyboard land" guessing what it is you are describing.
As far as an RV requiring money, in my experience that is a given....new OR out of warranty. On this trailer for example; before it left the lot I spent 1700 on upgraded tires and mattress. It is not quite 3 mos. out of warranty and I have spent approx. 7500 for new axles, springs, heavy duty MorRyde suspension and disc brakes....on a new trailer. Why? I felt when I bought it that the suspension was marginal and the more I towed it the more it worried me. Money; they all cost money to own.
Keystone quality? They're like every other brand of RV out there with the exception them make some of the best, best selling brands on the market. Do they have some issues from time to time? Yes they do but so does every other RV manufacturer in business today. In my experience they have done a great job of honoring their warranty
within the warranty period. Outside that time frame they obviously are very reluctant to just start repairing things for free because folks think they should; or their problem should not have happened etc. From the Keystone perspective the unit has been in service for months past the warranty period and they have absolutely no idea what the trailer has been subjected to. Just some thoughts on your situation.
I hope you find the solution and get it rectified quickly without costing an arm and a leg. And going forward just remember that examining every facet of the trailer every few months needs to become a ritual.....and that separate savings account for the RV needs to keep plenty of reserves in it for all "joy" of RV ownership!