Take the springs off and take it to another dealer. There is no way they are going to fix it with aftermarket springs on it. Be prepared to go all the way (legally that is).
BMW is usually easy to deal with, but the moment you have an aftermarket part within a spitting distance of a problem, they get ugly quickly - at least that's was my experience with my old E46. They didn't end up caring much about the motons, they just cared about the non-stock alignment and ride height.
Britax Carseat | Diaper Kit | Redneck Cutouts | Turner Studs | Bassified Individual Audio