Hi! and welcome to the forum!. I'm sure others with direct E9 experience will chime in. I have an E9 that is on the glide path to restoration as I approach retirement, but most of my experience is on an early 635, which has a similar front suspension and steering system.
Your photos ar a bit daunting. Not sure how far you want to dive in, but here are my immediate observations.
There is a fair amount of rust on the left side suspension components. It is doubtful they are rusted to the point of losing integrity, but in an abundance of caution, I'd probe them to be sure they have at least some integrity. Hard to see from the pics, but the nuts holding the tension strut, (the angled rod that end at the bushings and nuts that are prominnent in your photos) look like the nuts have corroded badly. But really the entire suspension subcarrier looks like it should be rebuilt, since replacing it in pieces seems like lot of extra work.
All that said, it is not clear if that would cause the problem you are describing. "floating" is not exactly descriptive. I assume that when you steer the car in some direction, it sort of goes there, but is not particularly precise. While it is possible that this is due to suspension members moving in their rubber bushings, it could also be caused by the multiple ball joints that make up the steering linkage, or it could be the steering box itself.
Here is a diagram of the steering linkage.
View attachment 199634
Any (or all!) of the various joint linkages in this system could be loose , or worn to the point of failure, and this would introduce play in the linkage and cause your observed "float"). I'd start by jacking up one side of the car. Remove the wheel and try rocking the hub back and forth as if the wheel was steering. if the linkage moves significantly, look to see where it is stationary. The other side wheel is presumably not moving, so if the jacked up side moves, you should be able to see what is moving and what is not, and from that determine if there is one or more loose joints. My guess, based on the look of the rest of the suspension) is the ball joints are all shot, and collectively they add a lot of play. One or more MAY also be loose (as in insufficiently torqued) as well.
In most cases on a car this old, it is easier to replace most of the moving parts. You can find many examples of this in the forum. But basically you disconnect the steering box from the steering linkage, remove the brake calipers from the steering knuckles (either remove them entirely and replace the flex lines and re-bleed after installation, or hang them out of the way in the wheel well). Disconnect the struts form above (in the engine bay). Disconnect the subframe from the car, and drop the assembly down. You can then either try to drag is out from under the car and disassemble it, or disassemble it in place on the ground under the car. Some of this will require spring compressors, some nuts will not come loose, and probably a few of the linkages will be unsalvageable.
Do some homework before hand and obtain the linkage parts you think will need to be replaced (tie rods, center link, bushings, etc.)and then you can cut the recalcitrant linkages with an angle grinder (likely to become a well-used tool!!) . Have the sub frame blasted, and check the integrity of what's left. Fix things like that broken tow loop, and then have the sub-frame powder coated, or at least painted with a high quality epoxy paint (as you can see, it lives a hard life down there!). While all of this is out, check the steering box and refit or replace as necessary (these do not seem to go bad frequently, so hopefully this is not the case here).
There are numerous threads here on re-assembly, including many on installing those big bushings at the front of the sub-frame. You may want to replace the springs while all of this is apart. My source for these part is Carl Nelson (La Jolla Independent), but you can get them from other folks as well. The forum is a great resource for sourcing parts. Clean and paint everything so that when it is all back together you will not want to put it in the car without cleaning and refurbishing the under side of the car and the wheel wells, and then everything else!!
) . Then you will have truly joined the madness!!
Good luck!!
Scott
