I'd agree that it's more often severe weather variations than maintenance that results in wood cracks. I have them on my low mileage 94 E500 as well and will just have to replace them. Luckily, it is not a huge cost (don't know the labour charges yet, though).

PS...the wood is burl walnut and, if you care to, the dealer will send a piece of your wood to the factory so they can match the color and grain as close as possible.