There are a number of potential trouble spots that can arise. I own a 2012 Regal GS which I bought in May 2018. The front headlight assemblies can leak, and typically cost hundreds of dollars each to fix. I replaced both of mine with assemblies not made by GM, because GM clearly did not know how to build ones that did not leak. There is a part on the turbo I had replaced (off warranty at my expense). There is the rear bearings problem, which I also had to pay to get replaced. I also made a choice to replace all 4 wheels and tires, because my GS had the cool-looking but annoying low profile tires. I got replacement 18" wheels, so that I could put real tires on it that don't blow out a sidewall when I pull into a Quick Chek parking lot. This was after I had to fully replace 3 tires that got blown out. And the Regal does not come with a spare tire - mine came with an electric air pump, but that does not help you if you blow out a sidewall of your tire. So I bought the "Modern Spare" kit which includes a very good spare which is almost as large as the regular tires, clears the front Brembo brakes, and yet still fits in the (previously empty) spare tire space in the trunk and allows the floor of the trunk to sit flat on top of it.
It's a cool car, that looks great and has an absurdly powerful engine. But a 2012 or 2013 GS is not a low-annoyance car. If you buy, just assume you will have to fork out extra money to deal with some of these issues after you bring it home.
I would assume whoever is selling the car knows how to disguise the leaking headlight problem (if that car has that issue).
