I disassembled an intermittent rear door latch from an '08 to try to find out what was causing them to weaken over time & I believe there is a very simple explanation.
You can see the small reversing DC motor here. It is held in position by two penetrating terminals that are underneath in this view. The terminals do double-duty as they also supply the reversing voltage by insertion into spring-loaded females in the motor body.
Here is a view of the inside contacting edge of one terminal (the other terminal looks the same on it's inner contacting surface). You can see the build-up of fretting corrosion on the upper contacting surface. Over time, as the corrosion builds up, the circuit resistance increases & the current flow across the surfaces is reduced. So the poor little motor gets starved over time & can't produce the needed torque to move the gear mechanism. It will work intermittently at times because that's the nature of a fretted connection.
I could not find evidence of any water intrusion or damage to the gears. If the motor had a harness connector instead of this foolish design, these latches might last ten years or better. I tested the motor & it's still produces a lot of torque.
If you were more careful than I was in removing the two rivets (there are also several small torx screws, but those are easy to remove) that hold the assy together, I suppose you might be able to refurb them by cleaning the terminals & applying dielectric silicone gel to them. Then replace the rivets with nuts & bolts.
Now this latch was from an '08 & I don't know if there has been a design change since then. There was a part number change at some point on the latches & that usually indicates a modification in design. This latch was part number 25919681 & has been superseded by part number 20922251. The same latch was also used in the Aura & Malibu.
Here's a good read on fretting corrosion: