Since you didn't mention the year your car was built, I'm not sure if my solution applies. However, I managed to do fairly respectable repair job on my "71 142, by filling in the cracks with silicone goop, trimming them as flat as possible after the silicone had set up overnight. Then I cut a piece of leather-grain vinyl a bit over-size in the fore-aft dimension and anointed it and the dash itself liberally, twice, with old-fashioned contact cement (the stinky, glue-sniffers-favorite variety). When that had dried to the point where it was no longer tacky, I covered the dash with some wrapping paper and laid the vinyl on top with about an inch of overlap toward the windshield. This I tucked under rhe edge of the dash pad, making sure it got glued on good and tight. Then I stretched the vinyl toward the dash face while also keeping tension on toward the sides so it would stay as close as possible to the winshield-frame/door-posts, gradually withdrawing the paper as vinyl attached itself to the dash pad. Finally, I stretched the vinyl around the front edge of the dash and trimmed the excess off with a utility knife. After blackening the edges of the cut vinyl with ink marker, you have to get pretty close to notice the repair. It's a finnicky job, but a lot easier than replacing the whole dash, if you can find one that isn't cracked. Removing just the dash pad from a donor is virtually impossible without ruining it in the precess.
Bob S.