Hello,
it is probably due to the leaf springs.
is it lower on the driver side? (were more weight is most of the time?)
A simple visual inspection should help you in confirming this. If you open the bonnet and look at the front leaf spring, you shuld see it pointing more down on the higher side, and remaining closer to the flat positon on the lower side of the car.
Leaf springs can be reshaped and reconditionned, and the car should come back orizontal. The User Manual gives the correct measurement for arching them.