I just looked at www.e38.org and down at the bottom of the page on the left hand side is a section titled "Air Conditioning". There are several articles dealing with the location of the high and low side of the system. Call your local dealer and find out which type refrigerant to use (older cars used a different type than that in use today, R12 I believe)....and then just buy it from them or from your local parts supplier.
You should troubleshoot the system to find out where your refrigerant has gone.
A forum community dedicated to BMW owners and enthusiasts. Come join the discussion about Bimmerfest events, production numbers, programming, performance, modifications, classifieds, troubleshooting, maintenance, and more! Bringing the BMW community together.