I had a Ventura rack fitted when I bought the bike new a couple of years ago and have been very happy with it.
Unfortunately the bag I have is a bit too fat to sit between me and the rack so it sits behind the rack and that adds weight to the back of the bike.
Last week a screw that holds the rack to the "L" bracket snapped and the spacer fell of and was lost. I searched the net for replacement screw and bush with no luck so I visited my local Engineer to have one fabricated. (Probably a lot cheaper anyway)
I am now wondering if the screw snapped because strain placed on it because of where I have the bag!
I have a Ventura rack and itís totally different than yours. Mine doesnít have that screw. The tail piece is is just a single none adjustable piece. The only screws I have are the ones which lock the tail piece to the main frame.