Ebay has the 2006 Buick Lucerne Owners manual for about $20.00
I had the same question and found this in the online owners manual. http://www.extendedgmwarranty.com/owners-manual/buick/2001-Buick-Century.pdf
Click the link I will post to view the owners manual online.
Ebay or you can download it from http://www.extendedgmwarranty.com/owners-manual/buick_owner_manuals.html
oops check with a buick mechanic,
its in the book owners manual
Read your owners manual.
Listed in your owners manual.
My car didn't come with a manual when I bought it, either (I have a 2004 Buick Rondez., too). A manual can be downloaded from www.gm.com. Click Owners at the top right, Click Sign up (it is free) and register your VIN. Once you register, click on "My Dashboard" and download owners manual. This worked for me.
check your owners manual i belive its 5 quarts
The procedure for doing this varies from manufacture to manfacture. If your owners manual does not provide the required instructions, I suggest you call GM, Buick division for help. The number is listed in your owners manual or you can find it at www.gm.com.
All the Buick owners manuals (1993 - 2007) in pdf format are currently available here: http://www.extendedgmwarranty.com/owners-manual/buick_owner_manuals.html Please note: I am not associated with this website in anyway... was searching for the same manual myself and came across the above link and thought it might help someone else in the future.