Re the tailgate strut, I had a similar problem on my 740. The stud with the ball screws into a captive nut welded inside the D-pillar. On mine, the weld had failed; as it gradually got looser and looser, it knackered the thread on the stud as well. I eventually fixed it with a "new" stud from a breaker, and a washer and LocNut.
Access to the back
is possible, but unfortunately, it's a stinker. If you take the plastic trim off, you'll find an access hole - but it's not near the stud, where it might be useful for access, oh no! But you can, just, get your hand in and up enough to get the nut started, and then get a ratchet spanner in to tighten it up.
But you'll end up cursing, with your back aching, your hand bleeding, and your head hurting from where the tailgate lands on it because the strut's not attached and you've just accidentally kicked away the broom handle you were using as a prop. Or at least, that's what happened to me...
