I will be very careful with that as any air in the system will be very hard to bleed.
Just do what I did on my old slk.
https://www.slkworld.com/slk-r171-class-diy/155170-diy-power-steering-wheel-fluid-change.html
from wis
Fill expansion reservoir (power steering) (1)
with MB steering gear oil Do not start the engine!
If the engine is started, there is a risk of air
entering the hydraulic steering, which is then
extremely difficult to remove.
Fill the expansion reservoir (power
steering) (1) up to approx. 10 mm below the
upper edge of the reservoir with MB steering
gear oil.
Refill with MB-steering gear oil continuously
until the oil level remains constant.
Bleeding
6 Turn steering wheel from steering stop to
steering stop Do not start the engine!
If the engine is started, there is a risk of air
entering the hydraulic steering, which is then
extremely difficult to remove.
Turn the steering wheel slowly from
steering stop to steering stop until no more
bubbles can be found in the expansion
reservoir (power steering) (1).
Repeat turning the steering from stop to stop
several times (up to 30 times). During this
process, MB steering gear oil must be poured
into the expansion reservoir (power steering)
(1) by a second person
Start engine without moving the steering Allow engine to run for Approx.. 1 min. at
idle speed.
During this process, a second person must
observe the oil level in the expansion reservoir
(power steering) (1) and add MB steering gear
oil as required.
8 Turn steering wheel from steering stop to With the engine running, turn the steering
steering stop wheel slowly several times from steering stop
to steering stop, occasionally adding MB
steering gear oil to the expansion reservoir
(power steering) (1).
Repeat the procedure until the oil level in the
expansion reservoir (power steering) (1)
remains constant and bubbles are no longer
visible.
Check
9 Check oil level in expansion reservoir (power
steering) (