Having taken two W201 dashboards apart (similar to the W124 design) it's my conclusion that the way they were built made them prone to cracking, from the windshield towards the seats. The dash is formed/stamped from thin aluminum stock, to which a thin coating of foam is applied just under the vinyl skin which again is heat vacu-formed over the aluminum shell. Expansion and contraction of the aluminum shell causes the cracks at weak spots in the covering, typically at openings, like the speaker and vent holes, or in gaps in the foam underlayment.

Avoiding sudden and extreme temperature changes will reduce cracking as much as preventing UV exposure. Use a vinyl dressing, as opposed to a product designed for leather, that will provide UV block, since it's nearly impossible to replace oils or "re-hydrate" vinyl.