I see that Porsche used Dextron 2 ATF in the power steering system until 1996, where they switched to Pentosin 11S (now 202). Most people on the board appear to use the Pentosin product regardless of factory fill.

Pentosin states to never mix CHF 11S or 202 with ATF fluids. Has anyone ever had a problem filling a car with Pentosin that had ATF originally?

My motors out so I had to drain the PS reservoir, just trying to figure out what to refill with. My rack and lines are still filled with ATF so I'm concerned filling the reservoir with Pentosin 202.

 

Having just spent way too much time with Pentosin over the past 2 weeks, I came across this piece of info in the service manual. Here it is, unfiltered.

* Porsche started to fill the brake systems with Pentosin CHF 11 S (green) in March 1996.
ATF was used before then. Pentosin and ATF are miscible. This means that Pentosin can be used to top up the fluid level in 993 vehicles before the aforementioned introduction date. On vehicles with Pentosin filling, always fill or top up the brake system with Pentosin.

Edit...with some additions

I recently had to flush some fluid out of my lines (different reason and different lines), but I was able to connect some 5/8" tubing to the ends of the rigid lines, then use a cheap fluid pump to pump fresh fluid through the lines. If you want to be completely safe, you could do something like this by disconnecting the PS lines in the engine compartment (so you don't have to figure out how to pump fluid into the banjo bolt fittings). Just a thought.