I just bought 5-5qt. jugs of Castrol fully synthetic for $16/5qts at my local Wal-Mart! Good shoping tip though, thanks for the heads-up. Not sure what the difference is between Mobile and Catrol, and I've read every oil thread and every link contained therein.
I do know my 14 year old 260E runs smoother with fully synthetic, and does not leak oil!
01 S55 AMG Silver
01 CLK55 AMG Silver