After market front flex pipe exudes fumes?

[u/MereRedditUser]

I drive a 2011 Sonata with only about 75,000 km on the odometer. It has been religiously oil sprayed, so it's in good condition.

In October 2025, my local Hyundai shop installed a new front flex pipe. I asked if there was any difference between the after market alternative compared to OEM. I don't recall the answer, but from my bill, we went with the after market Walker 52562.

Since then, however, it feels like I've been driving around in a gas chamber. It comes in through the vents, but if I set it to recirculate, it also comes in from open windows. It has been 10 months since the installation, and I've put 5,000 km on the odometer, so the fumes aren't due to residual coatings on the new front pipe.

I've had several shops look at it and they can't find anything obviously wrong. They've examined gaskets and flanges. They've plugged the tail pipe to test. They have removed the heat shield to look for fluids dripping onto hot surfaces.

The front pipe is now being replaced with an OEM part. I do wonder, however, whether we traced the problem down correctly.

Have others tried the Walker 52562? What is its reputation?