I have two points to add to the discussion.
First, Ken300D suggested cleaning the parts under (or is that above?) the pan when you have the pan off. I have consistently heard over the years that the pan internals should not be touched, no matter how tempted you may be, when the pan is off during a change. The filter is removed and replaced and the pan is put back on without touching anything. This is because you're more likely to introduce lint or dirt with the wiping than you are to remove grime if the tranny is seeing regular service intervals. I would therefore recommend not wiping the internals when the pan is off.
Second, for those that are both anal retentive AND obsessive compulsive, if you drop the pan, drain the TC, and break the fittings on the tranny cooler, you can get just about all of the fluid in an MB tranny. I'm usually content to know I got the TC and the pan.
HTH, not trying to start any wars,