Colt spent a lot of time checkering the stocks for their revolvers in the 1970's, it's too bad they didn't fit them better to the individual guns. I've seen plenty of loose ones, too; not just on the Diamonback but also on the more expensive Python.
If you want to go with replacement stocks, I've found the ones made for the Detective Special are more comfortable to use. Both guns have the same frame and will interchange. I never liked the shape of the factory-issue stocks on the Diamondback. I shot a .38 Diamondback with DS wood stocks back in the mid-1970's with modest success. Rubber stocks are available, too.
The Diamondback was a good gun that just couldn't compete (cost-wise) with the K-frame S&W revolvers. Collectors should be interested in the Diamondback some day. Colt didn't make a lot of them.