Iwould get the Mercedes Benz Interior cleaner/protectant spay (its made by meguires) and in addition to the cleansers it has quite a few oils and moisturizers to keep the material from cracking. As was mentioned also try to keep it out of the sun for most most of the summer (park indoors or facing away from the sun when possible.)

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Jason Priest
1999 E430
1995 E420 - retired
1986 420SEL - retired