Ah, Leather seats. I like to Detail my car, currently a Macan but looking at a GLC, and I found out that all these Leather 'conditioning' products are snake oil. Since 2000 or so, most leather in top end cars has been 'sealed' at the factory to protect it. If you apply conditioner, you are conditioning the sealant. I bet the handbook says wipe with a damp, not wet, cloth. I occasionally will use a weak liquid soap solution on my seats to get any dirt.
https://www.best-auto-detailing-tips.com/clean-leather-car-seat.html
PS That isn't me in the article!
https://www.best-auto-detailing-tips.com/clean-leather-car-seat.html
PS That isn't me in the article!