How much fluid should be put in the resovoir?

Mine has a little gauge with a min-max level on the
center stem. At the max, the resovoir is about
1/3 full.

Is there any problem with filling it to the top?

Also, if I have ATF in the resovoir and I suck it
out can I put the MB fluid in eventhough there may
be ATF further down in the system?

93 300SD -165,000 miles

Thanks.

__________________
Ralph Burnette
1993 300SD (286k + miles)
2000 SL500
2001 ML320