…. Is this correct and is there no way to seal from the outside? ...
The answer to that question is like many others: it all depends.
The rear edge of the oil pan on my Forte began to leak at around 40K and 2+ years. Turns out that the rear bolts were not torqued to spec. Don't know if they came from the factory that way, or just worked loose over time. As a result of the loose bolts, I could see that the factory RTV gasket had splits in 3 separate places, creating a very slow drip.
I'm the type of person who is militant about DIY, and never want a stealership messing around with any of my vehicles unless there's absolutely no choice. And I'd also read reports from others relating horror stories of the pan not being sealed correctly by their local KIA. One vehicle took 4 retries before it was finally done correctly!
But I also did not want to remove the pan myself while the powertrain warranty is in force, and risk getting a major claim denied. So I decided to try patching the cracks in the gasket externally with Ultra Black, along with torquing the bolts correctly. That was done around 60K miles ago, and the patch has continued to be very effective. Two of the cracks were completely sealed, and the third has just a very slight weep remaining. I do 7.5K OCIs, and never need to add oil between changes (yes, I do check the level regularly). So it's fair to say that there is effectively no oil being lost from the gasket.
But naturally I can't say this will work for your vehicle, because the specifics of those leaks may be quite a bit different than mine were. The key to determining if there's any possibility of patching yours is to completely evaluate the scope of the leaks. That means first getting all gasket surfaces completely dry, and also being able to get a visual on all parts of the gasket. A mechanic's mirror can help with the obscure locations. Once it's completely dry, you run it briefly and then recheck to determine the extent of the leaks. And of course, any loose pan/cover bolts need to be torqued to spec before this process is started.
One very important thing with your vehicle is to determine how much leakage is coming from the cover, versus the pan. The pan is certainly a much easier job, and less expensive if replacement by a shop is necessary. If it turns out that the cover only has a very minor weep, then patching it becomes much more feasible, than if the cover gasket has major cracks and leaks.
If you can't (or don't want to) DIY this job, you MIGHT find a good independent shop that would be willing to explore the patch option. And if no patching is possible, you can get a quote from them for the full repair, which I'm fairly certain would be lower than what the stealership gave you.