That is what is in the manual, but Porsche put out a TSB recommending changing to Pentosin. I'm still running ATF in my 968, but I changed over my 928.
Here is the TSB, it says 911, but the same steering system parts were used in the 968, and 944, the pretty much didn't care about those cars at that point.
Also it says you can mix, but I wouldn't do it, the ATF should be flushed.
Steering Gear - New Type Oil
Group 4
Number 9606
Model
6 Cyl.
Part Identifier 4800
June 11, 1996
Subject:
New Type Oil for Steering Gear
ATTENTION:
Service Manager / Service Technician
Model Affected:
911 Carrera 2 and 4, Model Years 1989 to 1994,
911 Turbo, Model Years 1991, 1992 and 1994, and
911 Carrera (993) 1995 Model Year on
Concern:
In production, the power assist steering system is now filled with Pentosin CHF 11S fluid (green in color).
General Information:
From the following VIN numbers, the power assist steering system is factory filled with Pentosin CHF 11S fluid:
As of March 25, 1996 from VIN:
99 9 TS 32 3082 Coupe
99 3 TS 34 1781 Cabriolet
99 8 TS 38 5439 Targa
Pentosin has been selected for use because of better and more uniform viscosity behavior at low ambient temperatures.
Vehicles of the model types affected produced before the above mentioned VIN numbers used ATF in the power assisted steering system. It is now permitted to use Pentosin CHF 11S in these vehicles as well.
ATF fluid and Pentosin CHF 11S fluid can be mixed. In vehicles produced before the above mentioned VIN numbers, Pentosin CHF 11S fluid can be used to top off the fluid reservoir.
The 1996 911 Turbo uses Pentosin CHF 11S fluid in the steering and hydraulic assisted clutch systems. In this system, ATF must not be mixed with Pentosin CHF 11S.
Vehicles having repairs made to the steering gear that involve loss of the steering fluid should be refilled with Pentosin CHF 11S fluid.
Parts Information:
Pentosin CHF 11S fluid (1 Liter), part number - 000 043 203 33
