I found a very thorough answer to this on Edmunds.com, check the 'related links' below. This is what it says:
Electric-/hydraulic convertible top pertains to a closed hydraulic system. As a rule, a filling is only required after opening hydraulic circuit (e.g. after replacing parts).
Remove CD player if installed.
Remove screws of left luggage compartment trim and remove trim.
To fill, convertible top must be opened, actual oil level can only be determined when in an opened state.
Remove oil filler plug.
Oil for convertible top hydraulics: G002 000.
Top off hydraulic oil only until oil level is between "Min" and "Max" marking.
Use a fill container for filling hydraulic oil.
Fill container must only be used exclusively for this purpose in order to prevent hydraulic oil impurities by other oils.
Screw oil filler plug tightly (5 Nm ).
On my 1998 E320 the power steering fluid is supplied by the load leveling hydraulic fluid resivoir.
I was a Merecedes mechanic. My 1998 E320 has an automatic load leveling fluid resivoir. This also suplies fluid to the power steering. I buy replacement hydraulic fluid from the dealer.
I was a Mercedes mechanic. My 1998 E320 wagon has a combined hydraulic fluid resivoir for the automatic load leveling and power steering. I buy the fluid from a dealer.
show me where to add power sterring fluid to my 1999 beetle
power steering fluid resivour
Plain regular power steering fluid.
You can use Mobil 1 synthetic power steering fluid for a 1999 BMW 528i.
Left hand side of engine compartment between finder-well and firewall
According to the 1999 Ford E-350 Owner Guide ( Motorcraft MERCON automatic transmission fluid ) is used as the power steering fluid
Germany
The power steering fluid reservoir is located next to the oil filter on a 1999 BMW 540i. The reservoir will have ATF written on it.
At the power steering reservoir.