I would not rely on the wing or fender as your datum.
On an absolutely flat surface, measure the distance of the bottom chassis rail to the ground. If you have 3/4 inch variance then start looking at the condition of the rear springs as it's possible that a leaf has broken. Broken leafs can be sometimes hard to detect.
The other cause might be a twist in the chassis but that's only likely if the car has been dreadfully mis-used or been involved in an accident.
How does the car drive?
You might want to measure ground-to-top of the body above the wheel or centre of wheel-to-top of body.
