how can itell if my mono spring needs to be replaced, 78 l82 and where is the best place to buyone if in fact i need one thank you mytoy

If it's sagging evidenced by the car being too low.wheel camber beyond the adjustments,constant bottoming out on minor bumps, Since something made you ask the question it probably needs replacing. Any of the vette stores;Corvette central,Eckler's,Mid America and others. My recommendation would be to go with the kit that puts composite monoleafs on both ends of the car along with the shocks to go with them. I did this to my 79 using the softest springs and heaviest ant-roll bars available. I have one of the nicest riding vettes ever and I may have improved the handling significantly.
Ron