The S54 M-Z3 uses the dual center over clutch pedal spring.



The S52 M-Z3 uses a single center over one shown with the from 3/97 mounting parts.



This pic shows the same spring with the up to 3/97 mounting parts.



The non M's use an extension return spring. My ti uses the same spring.



The pedal has never squeaked and the pedal doesn't take a set to the left like the ones that use the center over spring (especially with stock bushings). It stays centered on the clutch stop.
I finally got around to installing one in my coupe a few days ago. Pedal force appears slightly more. Driving with it is fine. Easily changed with a different spring if you wanted to change it either way.
If you want to try this, extension spring part number is 35 21 1 158 489. You also need two grommets 35 31 1 113 725 where the spring mounts on the pedal and pedal mount assembly.
The E46, Z4, X3 and the new one series use an extension return spring too, but it is smaller.