SORRY FORGOT TO SAY THIS IS FOR THE E90 3 SERIES MODEL (please put back in the E90 Technical forum)
After having suffered a rear LED light cluster failure as fitted to the LCI's i was quoted £256 for a replacement at the delaers, due to what looked like 3 failed leds in the turn indicator (causing blown bulb warning light on dash) which had it been a normal light would have cost me 3 quid for a new bulb i decided to take the light apart and investigate the issue.
This is what i found :
after you remove the clustser from the car you have to remove the plastic lens very carefully using a heat gun and a wide bladed screwdriver or similar, then you can unscrew the light boards which will then pull through the lens side of the light, once removed i tested all the resistors which were all fine, i then checked the voltage at all LEDS and found the centre board which contained the 3 failed leds, was pulling the voltage down to 6 volt, from 12 volt, i then checked each individual leds and found the top led to have failed and the others were fine, i replaced the failed one with a new 3 pence led of the same type from ebay (slighty diff shade of orange - but looked the same through the lens) this immediatley took the voltage back upto 12volt accross all leds and the light then functioned as it should do, Fixed at a cost of 3 pence and 60pence delivery ! BMW are a proper rip off for parts !
Seems to be a very common problem with the same led's failing and it really is an easy fix for anyone with a little knowledge and a decent soldering iron, i can post pics if anyone is interested