First gear uses the largest band in the transmission as you need a lot of torque to get going. Sounds as if the piston that applies this band isn't working properly.
The piston has a "teflon" seal & there are various size adjustment pins to change the band clearance. FIND a local shop that will try to replace this seal & adjust the band(in car).
Should be able to do this in 2.5hrs & $25 or less in parts.
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)