5 speed transmission(1 - 4/D(left right toggle).
I can't check the fluid level S-500's don't have transmission dip sticks(at least that's what the manual says, and I could't find one)
but I'm willing to be told different.
I had a 60K service done at a Mercedes Service Center, and they were supposed to have replaced the filter and fluid, but I didn't actually see them do it.
Engine check light is not on.
Problems are intermittent but seem to be happening more often.
Probably a good idea to see if any codes show up on the computer. They can check transmission faults?