Check out
this thread.
There's likely something loose around the bottom end/mirror cell, or the secondary holder, or screws/bolts missing altogether, but you had better rule out the mount for any/all of the shakiness by resting the tube somewhere solid and seeing if the alignment (collimation) still changes when you rotate the tube. Check for movement of any part of the tube and optics. And if the mirror cleans up OK (instructions can be found on IIS also), and the optics are of good origin as per the linked thread, then it's worth fixing. Also the spider is what you
should see when looking down the focuser without an eyepiece in it.
You could always chuck it on a dob mount and have a pretty capable allrounder.
Oh, and
to IIS!!