1999 996 tiptronic ATF Questions

[motolz]

I was getting a small leak from my transmission and it seemed the gasket was seeping and when I took the pan off, there was a crack in the gasket. Good news! I searched the forums and couldn't find a good answer for the following 3 questions.

1) what is the preferred after market ATF for a 1999 996, preferably from Pelican Parts. I found a variety of answers but am skeptical so I figure I would put this one out there

2) I understand the filling method, but what is the capicity...ie how much should I buy? 6.5l?

3) the ATF was done last year by my indy and he replaced the filter (maybe not the gasket..I don't know). I know that one should not mix ATF fluids. Do you think that there is enough of the OLD ATF in the filter to make a difference regarding 'mixing' ATF?

So can I leave the filter (the existing fluid was quite clean) and just put in new ATF that may be different from what I had, or should I replace the filter too? It has been drained for a couple of days at this point but just not sure if the residual in the filter would be enough to cause a problem. Thoughts?

Thanks all!