I've never injected a butt. I do plan to inject the next one I cook. I happened upon a show on FLN called 15 Bodacious BBQs & there is one segment with Myron Mixon. He shows how he injects butts & chicken. He also marinates his ribs in the same mix. While I'm sure all the "secret" ingredients were not revealed, it does give the basic for his marinade. It appears to be equal parts (about a cup) of La hot sauce, apple cider vinegar, lemon juice, light brown sugar, worchestershire sauce, and OJ with a gallon of apple juice
If you have FLN (channel 113 on Dish Network) they replay the show often.