Grimmspeed Exhaust Gasket Set 2015-2021 WRX / 2014-2018 Forester XT

I had already installed a full Invidia system on the car, but then had to go back in and remove the down pipe when I bought a set of headers. The gaskets in the Grimspeed kit are an MLS type gasket, way thicker than OEM (and the Invidia gaskets). With a turbo car and stainless pipes, you're going to have a lot of heat and expansion. Guaranteed these will hold up better over time over the stock gaskets. Easily 2x as thick.

So I installed these gaskets back in February. 2021 WRX with less than 1500 miles currently, aftermarket headers, titanium exhaust studs for the entire exhaust system, and a full Invidia exhaust.
After about 2 weeks of driving, I put the car back on the lift (car only had 1200 miles on it at this point). I wanted to recheck all the nuts/studs and make sure nothing needed to be retorqued. All seemed OK, and didnt take much more than 1/8 of a turn.
Fast forward to early May to my scheduled dyno tuning session. The guys couldnt figure out why the boost wasnt hitting where they wanted it.
Further inspection we found the gasket seal from the manifold to the cylinder head was leaking on both heads. Check the nuts, all tight and torqued.
Removed the manifold and turbo, found all 4 head ports leaking past the gaskets. Reinstalled with OEM gaskets. No leaks.
Back on the dyno, no leaks. Spun the rollers to 373HP/357TQ on a Mustang Dyno.