[MBZ] Rear End tilts down a bit on Left side

[Bill Gallagher]

It happens most of the time....notice the rear end is tilts downward 
about 2 inches when parked on a level surface ....but some other days, a 
rare few now, it is level ..... I changed the hydro fluid and filter 
about 5 months ago and now the fluid is blackish in color.
   Have not made a visual inspection ..... What's the possible 
culprit(s).... TIA

Bill
1981 300 TD