A build-up of engine oil sludge on early FSS-equipped vehicles was the subject of the infamous class-action lawsuit against Mercedes-Benz, which they have now agreed to settle.
In particular, the reliance on conventional oils recommended by Mercedes and very long oil change intervals indicated by the FSS system was leading to engine damage. Mercedes quietly changed to synthetic oils as recommended lubricants and, in harsh climates, now recommends more frequent oil changes than indicated by the FSS system.
You may want to check out
http://www.jacobsenlaw-pa.com for details...you won't get any info from your Mercedes dealer.
