I've never tried to repair the cluster on my e30 but I have replaced them as it was cheaper/easier for me. Here are some links I had saved that may help!

http://www.beckerelectronics.com/SIboard/Step_1.html
http://www.unofficialbmw.com/speedo/speedo_d.html
http://www.unofficialbmw.com/speedo/speedo.htm