JUst did the fluid and filtr kit change on my 300D.
Fun but messy job...
You are fine adding the last .6 or so litre with non MB fluid.
(That's what you meant right?)
Just be careful to not add too much would check/ recheck on fllat surface after a 20 min. drive....then if needed add a little at a time.
Since you're adding 6 qts you are draining the torque converter too??

__________________
'87 924S
'81 280SEL

Sold ->

81 300SD -
93 300E w/ 3.2
85 300D-
79 300SD
82 300CD
83 300CD - CA
87 190E 5 spd
87 Porsche 924S

"..I'll take a simple "C" to "G" and feel brand new about it..."