MB recommends Dot 4+ in all of their cars. Don't mix fluids & never use fluid that the container has been open(ed) for more than a year. Even with the lid on.
IF the brake warning lamp comes on, the pads should be checked & if they are OK then possibly you have a leak.
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)