The "spheres" or suspension accumulators are bad. They do act as shock
absorbers. Changing them is going to be expensive but not as expensive as
trying to add shock absorbers.

You would not want to change the system anyway as it would affect the
safety of the vehicle.  One of the advantages of the load leveler
system is that it keeps your car at its optimum balance regardless of
load.  Your car rides level whether you have 1 person or 7 in the
car.  The accumulators are not terribly expensive, but if you don't
change them the seals will blow out in the hydraulic struts
themselves, and they are very expensive.  You can get accumulators
here for about $105 each:

http://replacement.autopartswarehouse.com/parts/autopartswarehouse/wizard.jsp?ye
ar=1982&make=MB&model=300-TDT-001&category=All&part=Accumulator&dp=false

You need two.  If your car is bouncing, both are most likely gone.

You should change the fluid and filter in the system annually.  You
can use automatic transmission fluid instead of the expensive
hydraulic oil Mercedes sells for about $20 a liter.

Paul