According to the german Porsche forum and Tim Eckard who invented a presuized flush system the 986 and 986 AT ATF can be flushed with the engine and transmission in the car. But it is not that easy to do. Tim Eckart offers special adapters for his system.
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Tim Eckart is like Jake but for pressurized ATF flush systems over here in Germany.
Regards, Markus