I don't really inject turkeys that much. They have plenty of fat and come out tender and juicy if not overcooked.
If I were going to inject, I'd use something like:
1/4 c. water
4 T. Worcestershire sauce
1 t. garlic
1 t. onion powder
1/2 t. sage
1/2 t. thyme
Bring mixture to a boil and add 1/4 c. corn oil. Let cool, strain and shoot.