Place the butter in a saucepan over medium heat and cook until just melted. Do not let it turn brown.
Off the heat, add the chicken stock, lemon juice, Worcestershire sauce, onion powder, garlic powder, and Kosher salt. Whisk until everything is incorporated. Let it cool for a few minutes. It doesn’t have to be cold, but rather just close to room temperature.
Place the injector tip into the butter mixture and pull the plunger back to fill the syringe. If the mixture separates, you can “agitate” the butter solution by plunging back and forth a couple of times to emulsify and incorporate all the ingredients.
Prior to injecting the bird, make sure that any air pockets in the syringe are removed. To do so, point the syringe upwards and gently push the plunger until all the air is extracted.
Inject the marinade into the bird (you can start from anywhere) by inserting the tip at a 45-degree angle, distributing ¼ ounce per site at least 1 inch deep. You can start to pull the tip out as you slowly inject, but do not force it. Stop the injection just before you reach the skin.
Continue this process throughout several areas of the turkey, including the wings, breast, thighs, and legs, for a total of 20 to 24 times. Don't be tempted to massage or distribute the liquid because it will self-absorb as it rests in the fridge. If you notice the solution escaping from a different pierced area, apply slight pressure using your finger to prevent the solution from oozing out while injecting it into an adjacent area.
Once your turkey is fully injected, loosely cover it with stretch film and refrigerate it for 4 hours or overnight (no more than 36 hours).