An 8 hour drive to get it fixed it totally out of the question, but I'm glad you reached out to them to see how they will handle the situation.
Most RF cookers should hold MUCH better than 25° left to right, so there are a few things you can do to easily change that temp difference. Most people (myself included) started off with the cooker perfectly level, but that's not always the way these RF cookers are designed. Try adjusting your trailer jack so that the end opposite the firebox is just a few degrees negative from level...ie lower the trailer jack just a bit and see if that evens things out.
LOTS of physics going on inside an RF cooker, but the gist of it is that by lowering that end of the cooker you're forcing hot air to go down (when it likes to go up), and therefore you're slowing down the flow of air a bit and in turn it should help to even things out a bit.
* Is the firebox end hotter or is the trailer jack end hotter?
Personally I wouldn't worry about sealing anything...with a good seasoning and a few cooks most of those gaps should take care of themselves.
And don't beat yourself up about not inspecting the cooker properly. Nobody would be able to catch everything in all the excitement. The great thing is that cooker should work just fine and make some mighty fine BBQ, so don't sweat the small stuff.
Good luck and I hope they help you out in same manner with the fix.