[note: this post, like an air-cooled 911, is back-dated to when these events occurred]
I pulled my gauge cluster to address an erratic coolant gauge and a flickering brake lining light. I've not done this on an M3 before and it was very easy.
I was impressed when I bought the car that the "Check" warning light wasn't illuminated. Go figure, there was no bulb. The check panel doesn't throw any warnings though so I'm not sure why this was pulled out.
I can't harp on whoever did that too hard though, because I decided to follow suit for my brake lining light. I needed a bulb for the Check light, I was tired of the flickering lining light, two birds one stone. Easier to do it this way and just check the brake pads during normal maintenance. Pot, kettle.
While I was in the neighborhood I saw a warranty sticker on the SI board, with the phone number matching Bavarian Restorations, so it seems the board has been serviced already - nice.
Following a YouTube guide, I scuffed up the coolant gauge posts and put everything back together. The posts 'seemed' clean enough, but you can see that there was a big difference before (right) and after (left). I test drove the car this evening and the coolant gauge seems to be back in business. Not a gauge you want working intermittently.