Engine core line- and I know nothing

I have a 2012 Jeep Grand Cherokee and have no knowledge about engines, except how to check the oil and other basics. Took my Jeep to a chain oil place last month and had routine things done, nothing major. There's been a slight oil leak under the engine since then and the oil level dropped (obviously, but I wanted to mention that I did check and add oil appropriately). So I was thinking loose gasket or something from the oil change. They finally had time to let me come in. They said it wasn't a loose gasket or an oversight on their part when they changed the oil- my engine core line was rusted and wet, leaking oil. He needs to pull in the parts from the dealership to replace, for a couple hundred bucks. I had never heard of this, but as I said- I know how to start the engine and that's it. I've asked a few more knowledgeable people and they said it sounds off. Other items to note: the oil leak has disappeared since I took the Jeep back, and the check engine light turned on as I drove home from the mechanic. That is probably unrelated, but it didn't help my opinion.

He's getting the new line in this week and wants me to bring it back in. Can someone tell me if this sounds like it makes sense? Mr. Google hasn't been very helpful at all. I'm fine to spend the money on a repair if it's needed but I also kinda wonder if they didn't find a loose fitting and fix it, and are claiming this repair is actually the problem. I would have been fine if they had said that's what happened, and that the line still needs to be replaced. I do want to take it in for a second opinion but can't take it in until early next week for that. I'm sorry if I sound like an idiot. This is not my area at all. Thanks!