There isn't a 13 month limit - that's for sure. I've got a low mileage SLK230 and the FSS is pretty steady on the mileage count - looks like it ignores the time. That is why I would like to do an oil and filter change before it's due - too long between changes if I follow the FSS.

The engine types that are being mentioned - what type of engine does my car have? (Excuse my ignorance ... I'm a new owner)