I would make another attempt with Thor Customer Service. Sometimes you get a person who doesn't have good customer skills or is lazy and does not want to do the work to escalate an issue.
Be polite and present the facts and follow it up with a letter as well. Document as much as you can with pictures, etc.
I would do the same thing with your dealer. Get them to push the issue with Thor so you are attaching the problem from two sides.
If Thor won't due the right thing, try working with your dealer. Maybe they will split the costs with you or they will cover parts while you cover the labor.
All that being said..... water intrusion is a constant battle with these rigs and water can do a lot of damage. On my coaches I end up cleaning the roof soon after purchase and laying down Eternabond tape over all the Dicor and every seam, vent, ladder mount, etc. Eternabond will stop / prevent any leak permanently and limit the need to continually inspect the roof and constantly adding Dicor in places.
But you can't stop there. You need to look at all the vertical surfaces that could have an entry point..... water tank cover, furnace cover, slide moldings, ladder mounts, etc. You should inspect and replace sealant at least once or twice a year.
Then you need to inspect and protect your slide seals regularly as well with an appropriate conditioner and protector.
Unfortunately, there is a lot of maintenance with an RV to prevent water leaks.
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