it's even more complicated than that i'm afraid... i have the same cluster and i've looked into this a bit. there is no coding plug on our clusters - i managed to find one with a white back that works in mine (from a 525 auto) and before i hit 299960km i'm going to try and recode the plug on it somehow following the info on this site...
go here look under 'electronics' and '299960km' .
http://bmwe32.masscom.net/
good luck!
*- if you get deep enough into that site you will come across a page translated from russian by a computer, it's pretty funny....
"One of the big problems arises at replacement and repair shitkov devices. I shall describe some nuances below.
1. BMW525i Simens ROM X2402PI
This machine has very whimsical character, for the first time we have collided(faced) such problem when to us there has arrived the machine with dead shitkom, with inscription CODE pleasing an eye. Running forward, I shall tell, the reason in long ignoring inscription INSPECTION, and chasikov before the person of the driver."
... oh yeah!