As Haasman said, 'vertical play' under load suggests balljoints.
The strut mounts will outlive 2 sets of balljoints, based upon my observations.
I would bet that the movement you observe at the strut mounts when 'bouncing' is normal. The ones on my 124 are quite new, and there is visible movement similar to what you have described.
Best of luck.
1986 300E 5-Speed 240k mi.