Mercedes use electronic gear oil and at every 50-60k kms it needed to be changed. While changing that you need to change the gear filter as well. If gear oil and filter is old then it will develop leak in the sump. Which in your case must be there from sometime like drop or two everyday but you didn't noticed. And now when you come back from vacation that drop or two at same place seems noticeable + plus with continuous leak must have increased in 15 days too. So nothing to worry just get the car towed on recovery truck and get the gear oil changed. Also get the gear oil sensor change, i think (im not sure) your car has gear oil sensor too. Just double check that.
