For me, one big cause of weldment fealure on nice looking stuff is they weld with a minimum of added material. The weld joint smaller than the tube itself. I remaimber a nicely done SS pipe I purchase many years ago (from sector... Larini I think) lasting 45 min on track. Since that time, I am back to old school by doing my exhaust weld my self, I am not a welder, I am not very good either, they do not look as great as nicely look weld, but it last... I have now a K20 turbo with a full custom exhaust homemade since more than 2 years, no crack and no trouble, and big welding joint and not looking good.
I do not understand the obsession to make very thin weld joint on exhaust stuff.
On motorbike, the OEM TI exhaust line are lasting...
Elise 2006, white, K20 turbo GT3076R, 395 whp
List of mod: I am just stupid putting that much money on that car!