Last weekend I took my 83 928 off the winter jack stands ( the car is laid up from November till April ). I measured the bottom of the front ground effects ( spoiler) to the floor and got 8 inches. I took it for a ride and re-measured and got 6.5 inches. About an hour later I measured again and got 4.5 inches ! Do the struts have an internal leak ? Thanks.
Pretty much normal for a 928. You have just learned why you CAN NOT align the front suspension if the car has been jacked up to check the suspension...
The only place to accurately measure the front ride height is at the small machined flats on the caps that hold the rear of the lower suspension control arm. The height from the floor to the flat should be 170mm - 190mm per the factory workshop manual. Some folks run as low as 150mm - 155mm, but 160mm - 165mm seems to be a good point. Much lower than that hurts ride and handling to some extent.
BTW - A hydraulic leak would only affect shock absorber action, not ride height. The car's weight is supported by the coil springs - no hydraulics involved.