Well...you are doing all the right things so far --- but, if you have even a slight bit of rear toe out the rear end will come around on you (I think this is right - someone speak up here) --if you feel the rear left is lifting on hard turns then I would look at spring and shock replacement -- and even sway bars can weaken over time - and you have 89K on the car.
IIWM -- I would take it to a Porsche suspension specialist - if you have one in your area - I found one here in Phoenix after talking to a lot of people and finally a friend found this guy in a one man shop that mostly works on Fcars
Take care,
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