You can drain the PS from the steering box and get a clean flush very easily we discuss this on this thread: http://www.peachparts.com/shopforum/showthread.php?threadid=59076
hope it helps. By the way I have used both ATF and PS fluid in older cars. I concur with LArry if you have the choice use the PS fluid it is not that expensive and was made for this purpose.
m

__________________
Martin Ingram
Colorado Springs
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)