Long crack in Corian-like shower wall
About six months ago, I had the shower wall repaired by a Corian expert. I had a crack running from the shower control valves opening, through a screw holding the grab bar, up to near the top left corner, apparently stopping at the shampoo shelf. The expert removed the entire slab and repaired the crack. He thought the problem came from the screws biting into the Corian instead in the wood, so made eye holes in the Corian larger, and beefed up the wood before putting it all back together.
Now the crack has reopened, and goes all the way to the top edge. Even the shampoo shelf is cracked.
Is this a common problem, meaning another repair or even a new slab would crack?
The main question, is how best to get this repaired. What are my options? I'd prefer to have it done locally in Southern California, but could take it to Nac much later this year.