I have a nice set of old MOP S&W grips, but one grip has developed a couple of cracks (fissures) at the natural grain lines from the edge of the grip going into the natural fault lines in the grip. (crack/fissure - following fault line)

No chips or material missing on the grip. Is there an acceptable way to stabilize and or fill these cracks ?

Get an ultra thin sheet of plastic like they include with a cell phone case (a screen saver sheet) and use Professional Grade Super Glue from Locktite brands. Use a super thin coating of the glue to adhere the plastic sheet to the back of the grip panels. It will not really repair the cracks however it will keep the MOP grips from falling apart into pieces.

After you stabilize the grips I'd use them for display purposes only and refrain from firing the gun with them on. With a bit of luck, they will stay together for a long time. That's the best advise I can offer.........