Lowering a car causes the suspension to have a negative camber. The w124 cars can easily be adjusted for camber correction in the front suspension which is what I believe has been done to your car when it was initially lowered. Adjusting the rear camber on these cars is very difficult as it only allows for very small correction which would not be enough if you lowered your car pretty much. This is why your front tires don't wear out as much as your rear tires. Assuming that all your rear suspension components are in good condition then one way of correcting your rear camber problem is by getting an adjustable rear camber link which allows for a greater correction of rear camber specifically for lowered cars.