I am not 100% sure if the steering and suspensions are the same, but when my W124 became more difficult to steer, the cause turned out to be bad ball joints, so i guess it couldnt hurt to check them out.

As for the PS fluid , i would go with the MB power steering fluid, see your local dealer, its pretty cheap. If you do not know when was the last time the fluid was replaced, compare the PS fluid in the pump reservoir with some new fluid, if they dont look the same, then replace the fluid. In your case its probably best to just wait for when you decide to replace the leaking PS hose, and then put in a new filter and fluid.

The PS fluid in my car now is pretty brown, and im pretty sure that its not supposed to be that color . Even though its brown, its still pretty eaasy to steer and the PS pump does not groan one bit. I plan on picking up 2 liters of the MB PS fluid, a new filter, will then pull the PS return line and flush the complete system. i think that the procedure can be found in the DIY section.

good luck