sounds like the rear height corrector is stuck try spraying it with wd40 to free it off, this is very common prob on xantias usually seized cos of its position wher it collects all the crap off the road, salt, grit etc , this controls the ride height of the rear of car and is linked to the hi/lo lever check all linkages to rear height corrector (sometimes the linkage can pop off) most of the time they can be freed of easily enuf, once freed off ensure u do a hi/lo operation at least once a week and keep it lubed esp thru winter.
double o, February 2010