Your car uses a multi-function relay that controls the w/s wipers.
Next time that happens try removing that relay & see if the motor will park. IF so the relay is the problem, if not then the motor must be at fault.
That relay lives in the rear section of the fuse/relay box.
LOOK for MB part number 201-821-02-47, should be the 2nd largest computer in that area.
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)