the leak is slow and usually absorbed by the dust passing though/around the front of the engine, generally 10 years or more for the factory unit and less for aftermarket units i find for life span, the behr unit costs more but is much better then the sachs, theres a really cheap after market japanese looking clutch with a spiral spring in the front that is failure prone, a good portion of them lock up and explode the fan blade and others crap with no real leak or other sign