Bump as a couple of folk have asked about this fix (nice to know it's been useful)
LEDs.
These were a gamble but worked fine, search for "5mm high-intensity red"
- don't use ones marked "diffuser" (these spread the light - will they miss the lightbar?)
Each light cluster has 3 LEDs (12 in total for my E93).
I paid about £2 (including postage) for a pack of 10.
Glue.
Use any (I had some "Hard Plastic Glue" by Bostik, it worked fine).
Superglue? I didn't think this would fill all the small gaps, so I avoided it.
Time taken for each light : 1 hour strip/rebuild + 1 hour finding the dud LED and soldering.