According to the manual, you must do a deoil of the system before doing a citrus acid flush whether there is evidence of oil in the system or not. However, if the coolant in there now is nice and clean, then you probably don't need to do anything except flush it well to get all the old stuff out.

__________________
Len
'59 220S Cabriolet-SOLD and living happily in Malta
'83 240D 351,500 miles original owner-SOLD
'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
'99 E300 turbo 227,500 miles
'03 SLK320 40,000 miles - gave to my daughter
'14 Smart electric coupe 28,500 miles
'14 Smart electric cabriolet 28,500 miles
'15 Smart electric coupe 28,000 miles