I sent an e-mail to Leatherique company and got this response back:
All colored leather is surface coated. Since 1990 it has been a water based coating. The finish is water resistant, NOT WATER PROOF!!!! The Rejuvenator will easily penetrate the finish as will rain water, coffee, or anything else you spill on the surface and leave. The Rejuvenator is a natural water based protein collagen complex that will keep the actual hide, the backbone of the leather luxuriously supple and healthy. If you don’t do anything to keep the hide nourished, it will become dry, and the spongy fibers will pull apart creating cracks.
The people online who are spreading the rumor that leather is water proof are complete liars for spreading such stupid and misleading information. If this were the case, the car companies would use vinyl instead of leather. leather is a natural product that breathes and adjusts to body temperature, and feels soft and supple. If the consumer wants something water proof, maybe molded plastic seats would be better in cars? People want the luxury of leather, because it is a once living, breathing, fibrous structure, that does require some care and nourishment to stay healthy.
Since you own a convertible, would you leave the roof down and allow your interior to be rained on? Of course not, as the leather would absorb the rain, become drenched and shrivel from the heavy impact of too much water.
In the olden days that was how they created armor and shields, by drenching leather in water, letting it dry, so it was stiff.