Add oil to a bowl and stir in salt, oregano, garlic powder, rosemary leaves, onion powder and ground black pepper. Using a pastry brush, brush this mixture on all sides of the pork roast except for the bottom.
Place the roast into the slow cooker and carefully pour the broth around the outside. Cover and heat on high for 6 hours or until it is tender and center reaches at least 145 degrees F in the thickest part, center.
If you want to make with gravy you want to pour the liquid at the bottom of the pot into a small saucepan over medium heat until it bubbles. In a small dish whisk together 1 tbsp cornstarch with 3 tbsp broth until smooth, stir this in to thicken. Remove from heat once thick to your liking and pour on top of each slice when served.