I've had several Thor products, and several Forrest River products. In my opinion, they are about the same. Every RV I have ever owned had some really dumb mistakes in it's manufacture. Most I easily fixed, but I'm handy. If you aren't comfortable caulking, reinforcing, packing bearing etc, then RV ownership can be very stressful. I've had 13 RV's in my lifetime, and have never had one back in a dealership for repairs. It's my experience the dealer will not fix a problem as well as I can, and will cause some other damage while attempting repairs.
I live in a large city, and there are several respected mobile RV repair individuals. If I were not comfortable making repairs, I would establish a relationship with one of these folks. Sealing roofs must be checked and done properly yearly if your RV is parked outdoors. This could be done by one of these guys in one day, vs leaving it at a dealer for weeks and then having the trainee give it a shot. Same for wheel bearings, unsupported shower floors, plumbing leaks etc.
You didn't mention any other problems with your Thor other than the roof leak, which could happen to any trailer. I would advise buying the trailer you like, and finding someone you trust to check the roof when you take delivery, and yearly thereafter.
