They can fail. Failure often results in major differential failure that is remedied by replacing the diff. Farm the work out. When they start to get tired, they can be easily reconditioned by a competent overhauler. These are the biggest failure point.
Replacement can require a different crankshaft and block if the condition is severe enough.
To check, simply push the crankshaft pulley rearward as hard as you can, then have an assistant sit in the car. Now, use your hand to span the space between the crank pulley and the front of the engine, and inform your assistant to lightly step on the clutch pedal. You'll feel the crank pulley move forward slightly, and this will reveal the condition of the thrust washers. If the distance seems greater than say, the thickness of your fingernail, you should bargain for a lower price, knowing that you'll have to be into the lower end of the motor soon. In this case, a different engine would probably be in order.