Remember, FSS was designed in Europe (and consequently here) for SYNTHETIC oil. They let conventionals run too long and are causing all sorts of problems inside. 90% of these problems can be solved by just switching to a name brand synthetic though. I always tell people no more than 5,000 miles on conventional and 7,500 on synthetic (although if you drive on the highway a lot it could probably go much longer).
1988 Mercedes-Benz 260E