Bad experience
 

I replaced my CMI headers with salt water treated Hardin marine seaward manifolds rated for my 500 efi motors on my 38 Fountain. I flush religiously every day of use in brackish water and the starboard side sprung a leak into the engine compartment. Very disappointed as I had hoped to get a lot longer than 4 seasons. I will replace them with the same as I don’t want to RE-rig the boat but I would say a C- on longevity…

Hardin seaward

Four seasons?? That's a lot of cost to only make it so far. Isn't Stainless Marine five years? Looking above... the 14mm hex clues one into their origin.