Rear shock absorbers

When my mechanic had the wheels off my car to balance the tires, he said my left rear shock was leaking fluid and my shocks needed to be replaced. My car has air shocks. Do air shocks contain both air and fluid? I could see some fluid on the left rear shock but not on the right one. Also I could see a small amount of something caked on the left rear shock. In my investigation of several sites, including Car Talk, the articles said that a leak does not necessarily indicate a bad shock. Should I replace the shocks or are there other questions I can ask my mechanic or other tests that can be done? I’m not strong enough to push down on my bumper to see how the rear end reacts.

A leak pretty much tells you the shock is bad. There have been some discussions about how much weepage in shock action equals a leak, but it sounds like yours have reached the leaking stage. Air shocks contain an air bag to adjust height as well as fluid in the shock just like others.