The finger holes are fairly sharp aroung the edge and could use some beveling/sanding. This is one of the reasons balls crack around the fingers.
You can fix the situation by drilling out the cracks and plugging the fingers. Just because there are hairline cracks, doesn't mean it'll ever chip out. A good sanding/beveling might do the trick.
If you decide to plug the holes, the plug is weaker than the urethane and will be prone to chipping, especially if you're using "super glue" to glue in the grips. An epoxy glue is recommended in either situation, whether plugging or not. =:^D