Wondering the same stuff as Eric.
Another way to say it is did the primary circuit (the 'trigger' circuit) of the relay fail or the secondary circuit (the 'load' circuit).
That will tell you where the problem is.
In other words, if you remove the 'dead' relay from the circuit and apply 12V to the trigger circuit, does it still 'click'? If not, the relay coil probably saw too much voltage. You could check the car's wires that are connected to the relay's trigger circuit, with the engine running at maybe 3000 rpm, and see what voltage is there. If it's much over 14V, not so good.
If the relay still clicks but doesn't close the load circuit when it does click, the attached load may have shorted to ground at some point and burned out the relay contacts.
I have used a lot of the 'CCC' relays with no failures yet.