You can do a visual inspection yourself. This is an inspection of a 1980 model, but most models from the mid-1960's to the mid-1990 's have similar automatic transmissions and related components. This is something you should do after acquiring an old Benz or if you own one and have never done it.
Get a good light and get under the car.
W110 W111 W112 Sedan
W111 W112 Coupe