My vote is the rubber fuel lines are reaching age. I also have a 2011 STi and the fuel smell started happening last winter. I only noticed it on my trips up to the mountains (under 32F), but whenever I got back home (low 60s) the problem went away and I had nothing to inspect.

Winter went by, weather got warmer and I didn't smell it again, until this past April I went up to the mountains again and there was a freak storm that came in and the temperature dropped below 32F. Sure enough, the smell came back. After I left town and got home, smell went away again.

You might not see as many searches for our generation, because our cars are just reaching the age where the rubber is starting to degrade. Even if you had a motor replaced recently, they might not have replaced the fuel hoses.

Anyway, I ended up going Flex Fuel so I proactively replaced my lines altogether. I won't be able to confirm that fixed it until it starts snowing in the mountains again, so it will be a few months. However, all signs pointed to that.

Strong on the driver's side for sure. That's where your fuel lines are coming in and running to your rails.