I drain and fill the reservoir every 10k...seems to keep the fluid clean, and it's certainly easy. Will do filter maybe every 60k.

Humm, I have an old post from a guy on the MB news group that claims he opens the lid of the pump, drains the steering box and refills the pump, no problem. Claims the drain plug is "in the middle and aft and pointing slightly back on the bottom of the steering box", If it wasn't the cocktail hour I'd run out and see:D

There's one on mine. No sense in draining though, pushing a gallon or so through (wiki method) while turning wheels to the hilt slowly left, then right does the trick.

I've always just drained the reservoir, pulled the return line, put it in a bucket, plugged the return connector, filled with fresh fluid, then turned the pulley by hand until clear fluid exits the return line.
I've never turned the wheel lock to lock. I'm always afraid to let air damage the pump with the motor running. and it's difficult to turn the wheels without the motor running.

when I did mine I put the front end on jack stands, and with the engine off I turned the steering wheel back and forth. This cause the fluid to drain fairly quickly but was manageable with a gallon milk jug (in the place of the washer res.) with the low pressure hose stuck in it.
I went through 4-5 quarts including the what was left in there.