If you only used 4L of tranny fluid then you didn't drain the torque convertor and should do so as part of a complete fluid change. There is a total of 7.5L of fluid in the 722.6. FYI, you can use the most recent fluid for the 722.9 which is backward compatible to the 722.6 and it is a little cheaper than the original stuff.

Still you are lucky to have gotten it fixed as cheaply as you did, congrats!

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz