I couldn't believe it when I saw this topic - since I'm having this exact issue. A remanufactured steering rack was installed in August, and in the last couple of weeks, the "turning left" problem has started. It's only on startup in the morning or after the car has not been used for a good number of hours - so, it seems to be a "cold" issue. Here's what Zims (the source of my rack) just wrote back to me:
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I am sorry you are having a problem with one of our reman steering racks. We very seldom ever have an issue with our reman products.
We have had the same builder for many years. He does a great job for us and he is here local which helps.
I contacted him about this and he said, "It may have something stuck in the rack's spool valve". I noticed that you did not purchase a new filter/canister with the rack. Did you replace it, or at least take it off and clean it out? Porsche only recommends the replacement of it since the filter in the bottom of it is not removable. We at least like to see them flushed out and cleaned. The rest of the system must be flushed out to make sure there is no debris in the system as well. Was this done?
It could also be the spool valve itself or one of the Teflon rings never sealed properly. Did you have a similar problem originally or was it just leaking?
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Next week I'll be able to explore this a bit more.