Since this thread originated in 2010 I'm assuming the gun was bought and shot so that's that.

Information I've picked up on the 1911 forum indicates the weak point is the slide cracking due to the heat treating processes used thoughout their history.

They give a general lifetime of slides of approx. 1,000 shots for WW1, 10,000 shots for WW2, 100,000 shots for modern.

Once a slide is cracked it is toast so if the gun is an historical piece it's best not to shoot it. If you must replace your recoil spring and don't do a lot of shooting with it. You are rolling the dice.