I am a fat side down cooker too. I have not injected and like the results I get. If I was gonna inject, I would either just do beef broth or a pre-made like Butcher's or Kosmo's for a first attempt.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"I'm Armenian...perhaps...but then again...maybe not..."