I have to admit my basement concrete floor is not the most level but I've added pieces under the legs where needed to get it as level as possible.
I also wonder if maybe I'm putting my 3 layers too tight with the clips on the sides as well as while advancing the quilt as I do use the belly bar as I know you don't Dunster.
As for my leaders, they never were straight from the get go when installed back in late 2012. I decided after my last quilt was removed, I was going to fix that plus the back leader was starting to fray so it needed repaired anyway. I ran a straight line stitch across the bad leader, cut off the bad section, folded it over and believe it or not, I used staples to make the fold so I could install the red plastic whatever it's called that you clip the red snappers to. I also used, again believe me, I used that shiny silver tape they use on A/C duct work to seal over the cut edge as that tape sticks forever it seems. Anyway, my back leader is now straight. Eventually I'll order new leaders but for now, this jimmy rigged method will do.