If you have a w123 wagon with the Self Leveling System (aka SLS)you have what are commonly called "spheres" or "accumulators". There are two- one on both sides just forward of the rear wheels. If they "go bad" you have a bouncy ride that is horrible. One side can go bad and you still have a good side, and the ride will be worse than normal but not as bad as when both sides go bad. The ride quality can suddenly go bad, or breakdown over time. If you want to test to see if you spheres are good, here is the procedure:
Remove spheres from car. There will be a bit of pressure in the spheres, so wear safety glasses and watch out for/ prepare for some squirting fluid. Here is a removed sphere: Remove the banjo bolt from the sphere- Look at this picture:........
To test and find out if the sphere is good, find a rod that will fit inside the sphere, and see if you can push it down into the sphere. It should make contact with within one inch inside, and then be difficult to continue pushing in. If it is easy to push down the sphere is no good. If it is very hard the sphere is good. Inside is a rubber diaphragm that can and does fail- this is what you are pushing against. Do not use a sharp object to test, and this could puncture the diaphragm. ......When you re-install a good sphere it is self bleeding, to install and drive happily!