There shouldnt be any play at the ball joint. To test the ball joint jack up the car or put it on a lift and grab the tire at 9 and 3 o clock and wiggle the tire back and forth. Have an assitant look under the car while you do that. If there is movement then you need them replaced.

This is just general and maybe leaving some info out.

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)