On my friends, sisters 05 CLK320 you check the oil on the dash. Their is no dipsitck. Maybe this car is the same? The manual should say about what the engine holds, probably like 7-8 quarts on a MB V8. So just put 6 in, and see what the dash says.
As for getting the oil out, their has to be a dipstick tube somewhere?
I know the dealer doesn't drain it.