Drove about 200 miles yesterday and the exhaust smell has returned with a vengance.

plugged in the vacuum to the exhaust today and sure enough there is lots of hissing at one of the weld spots and lots more right at the turbo flange.

since I did not use the vacuum test when I left the muffler shop I can't tell if these leaks developed over time or if they where never addressed. but I could swear there was no smell for a few days.

It's possible the temperature changes as well as the rigidity of the flex pipe are causing the flange to become dis engaged under different driving conditions as I assume the engine does rock back and forth under load.

the original DPF did have multiple mounting bolts securing it whereas the Buzzken downpipe simply floats.

called the shop and they did say I could bring it back if any leaks develop so I will be taking it in next week.