Originally Posted by Arian

In this forum they suggest bending the spring into another hook, instead of buying the full $130 part. Broken trunk latch fix (easy DIY) - Bimmerforums - The Ultimate BMW Forum

However my occupation gives me some extra knowledge about spring... I'm a rocket scientist, structural engineer for Boeing, and we work with springs all the time. The thing to remember is that if you bend the coils to remake the hook, you reduce the shell life dramatically. I took my spring to work to see if my engineers could figure out if I could get an exact replacement.

They found the exact spring for my E53 at McMaster-Carr Product Number: 9432K32 mine was a zinc-plated steel music wire, it comes in a package of 6 for 10 dollars. This spring will be an exact fit instead of buying the $130 part, 51 24 8 408 492.

It's too late for me since I bought the $130 dollar part, but hopefully this well help others!