I selectively copied some information from a Newletter I get called Nutz&Bolts pertaining to transmission flushing.
I personally wouldn't use a flushing machine on a benz box, I would drain and refill, realizing that the first item listed below holds true.

1)The flush machine is only as good as the operator.

2)The flushing machine has an audible warning to prevent the machine from running the transmission dry - which can cause damage.

3) If care isn't taken dirt contamination could happen

3) Shop should be ATRA member repair shop.