If one wants to be a mechanic (or anything in life) one needs a credential. Mechanics have ASE Certification, doctors have MD degrees, scientists PhDs etc. That's what's needed to get in the front door!
Yes you can "make a living" without a credential but one is often at a disadvantage as others with the credential jump in front those without the credential. A secondary, cap-in-hand position isn't a winner - ever.
A youthful shortcut will relegate a lifetime of work to second class wages. That's not what you wanted to read but is the truth so don't take that shortcut. Mercedes and all cars are increasingly complex and beyond may of us who grew up in the 1950s and easily understand those simple, old cars. That's history, your life is the future don't shun the future act to take advantage of its opportunities. There's currently a shortage of automobile mechanics - my local M-B dealer even seeks mechanics in its mailings to us owners!
Cars are not the only mechanic jobs. Diesel mechanics, construction equipment, air conditioning (auto, and commercial) railroads, aircraft engines and aircraft all require certified mechanics. An FAA certified mechanic is a good job.