CJ, my opinion is that traces of the old coolant will be nullified by the new stuff.
With that application, coolant with coolant, trace contaminants should do no harm. The orange stuff claims to be basic coolant plus additives.
However, an earlier post by senior member
Larry Bible cautioned against using the same plastic funnel
that has been used for transferring coolant, for the addition of transmission fluid. In this scenario, trace
contaminant of coolant does not wash off the plastic
and , according to him, can cause very serious damage to the
sensitive Mercedes transmission. He's talking molecular level trace coolant elements screwing up a transmission!
Do a search!
Good Luck.

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD