Car leaning on one side (right side) when Parked

This vehicle has air ride suspension and you have an air shock leaking down either from a leak in the shock itself or a fitting

Will this require replacing the part (s)?

Most likely id say yes to replace the shock. Its always best if possible to replace them in pairs, both rears in this case. But make sure its not just a loose fitting first. Let it get to ride height, jack up the vehicle, take off the tire on the affected side and sprat water with dish soap in it and watch for bubbles. Spray it everywhere looking for bubbles. That's also good for leaking tires and fingerprints on the shiny parts. Lol