You need to sort out the play in steering linkage , before you go messing with the steering box, i took my W123 for mot i was told the steering box was worn and needed replacing ,,. Then a friend who new all about the W123 steering he said replace front steering linkages .I replaced all the linkages and car passed its mot after it was lined up the right way .Get under the car and ask someone to turn the steering wheel for you while you look for play in all the steering ball joints. If these are replaced do use a good garage that know all about the W123 if you dont you will have problems with indicators not canceling out as tou centre the steering wheel..