The rubber bond of the outer ring gets weak with age, so it becomes a time bomb "Powerbond" in Australia offers a variety of balancers, including SFI approved units at great prices.

If your engine is a big block, I have a brand new in the box TCI "Rattler" #870009. These units do NOT use a rubber bond or rubber ring. The housings are machined from one piece of steel, so there is no outer ring to break apart. They retail for about $400. I'd let this one go for $200 plus shipping. I have a TCI Rattler on my Hemi, and I love it! Bolt it on and forget it.

The ATI Super Dampers are very popular, and they use a rubber ring that they recommend replacing after 10 years... 'jus sayin'.