You can also get the suspension fluid right here at FAstLane ~$9/liter last time I saw it. Fluid should be changed every two to three years. The fluid on the 560 was very dark when I got it (instead of the amber boch color it should have) and the filter had crud collected at the bottom.
Change the filter and fluid, dirt and other contaminants can cause other problems in the leveling system. You don't want to buy a suspension pump at $500 or more or a set of rear leveling struts at a couple hundred a pop ( or a set of accumulators), much much cheaper to spring for 4 liters of fluid and $3 for a filter.
The fluid may not be subjected to heat like motor oil, but the pump is mounted dirctly to the block so the fluid is subjected to radiant heat. Any time the engine is running the pump is cycling fluid through the system, absorbing heat and continuously working. I think the system is high pressure/low volume, due to the fact the fluid only flows into the resevoir ar a trickle, but lifts/lowers the car instantly.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.