BMW Repair: What is a Guibo?, guibo, driveshaft

Question
I have a recommended maintance which mentions something called a "guibo" which is priced at $726.46.  I am trying to find out what is a "guibo?"

Answer
It must have a vibration.The guibo is the flex disc that connects the driveshaft to the transmission.The disc itself isn't that costly they are about $50.00(through bavarian autosports 1-800-535-2002)The labor is what is expensive as you have to remove the exhaust and loosen the driveshaft to get to the guibo.The disc usually cracks which is visible when looking at the rear of the transmission/driveshaft.