Mine went out several weeks ago at 78K miles while my wife was driving the car @35 MPH. My wife noticed a "strange noise" coming from the engine.
The noise was the drive belt being shreaded due to the balancer loosing the rubber ring causing the balancer shifting toward the engine block creating the drive belt to shread the inter two ribs. My wife was able to drive several miles back home.
After much trouble getting the crankshaft pulley bolt loose, I removed the crankshaft pulley to find a slight gouge in the timing cover. There was a very slight amount of oil seeping from the gouge. I applied some JB Weld epoxy to the gouge, installed a new crankshaft damper and drive belt and everything is back to normal.
I was fortunate that the crankshaft damper went at 35 MPH instead of 65 MPH. I did not loose the entire rubber ring, the ring looks like it sheared off leaving about 1/4" intact at the rear of the damper which kept the pulley assembley "together".
From my experience there was no early warning - I would replace yours to avoid potential damage.
If your car is still under warranty, I wouldn't hurt to ask the dealer if they are willing to replace it at their expense. My car is out of warranty so I replace it myself. The total cost from Partsshop for the crankshaft pulley and drive belt was under $100.
1998 Mercedes E320, 200K Miles
2001 Acura 3.2TL, 178K Miles
1992 Chevy Astro, 205K Miles