The seat height is operated off of a sprocket gear; you may need to remove the seat to fix it.
To remove the seat, look for the bolts that hold it in, they are inside the slider track four total 2 in the front and 2 in the back; once you have removed the bolts the seat comes out (some what easy, yeah rite!). Make sure that the seat does not get caught on the center console and be very careful not to bang it into anything such as the door, hallway and console, which by the way is very easy to do. If you have a heated seat you will have to, unplug the heater lines.
It also may be a good idea to stop by your local MB parts shop and pick-up some new guides for the seat rails, they tend to wear out over time.
Eric, 1983 500 SL