A good info from Thailand by by GRANDFATHER (Assoc.Prof. Boonchat Netisak), he is driving an E34 525 and has since years a DIY site
Switch Gear Clearning , D.I.Y. by Assoc.Prof.Boonchat Netisak
A lot more of good info on his site BMW E34 DIY by Assoc. prof. Boonchat Netisak