Hi 1998K, yes mine are both wood dash inserts, but the 1994 one has very straight parallel lined grains while the 1997 has a burlwood design with loops all over the place. Hope this pattern will prevent the very thin veneer from cracking. Our Summer here in Melbourne is very hot sometimes like 30 to 40C. Maybe the windows left closed makes the car become like a microwave which kills everything inside including the plastics and cloth seat material. I always thought there is a built-in air outlet somewhere which works automatically letting hot air out of the vehicle even with all windows closed.
My 1994 C180 is starting to have this problem since I started to park it under the sun, my garage is chock full. It seems that the variety of wood veneer applied to these surfaces are too thin and not suitable due to the wood grain. They seem to be cracking horizontally across the deck along the wood grain lines. Didn't the genius designers of the time in Germany ever think of this? Well, maybe they have colder weather, so it never happenned? BMW has learnt a lesson and are using "wood" in their newer cars. The latest 5 series come with such fake looking "wood" dashes that even I was shocked! You can see the perfect lines where the 2 different grain patterns meet! They look very plasticky too! I have seen many used cars of the 124 and 202 models with this wood veneer problem and it seems worldwide. Perhaps if it was thicker and of wood grain patterns that do not have any natural linear weaknesses, they would be fine. My 1997 C180 has a better wood veneer and does not have this straight line grain. Fingers crossed that this would last a lot longer. 
I've seen somewhere a kind of solar activated fun to install in a side windows, when parking the car under a hot sun this may permit a few air circulation. I don't know if this may help with 40°C.
