Porsche finally released the parts and diagrams for these transmissions, roughly a year ago. The article from Lufteknic is good, they know their stuff. Their website is not updated often though, and has not been updated for this issue though AFAIK. The G96 and G86 transmissions are now serviceable. And the parts are generally more affordable and available than a corresponding G50 component.
Re: the failures mentioned by Lufteknic, since there are over 100,000 of each of these models out there, with larger numbers come more problem reports. With ten times as many units on the road, I would expect to hear of ten times as many problems. By percentage these are still reliable units. Some may wear out the main bearing faster, but so can G50's -- Porsche says to check the race gearboxes every 30 hours. All gearboxes need maintenance, so why not use one that is more plentiful and easier to service or replace?
A replacement G96 gearwheel for example is $200 to $300 new from any dealer. That beats $1000+ for a matched-pair-only for a G50. Also some of the G50 gears have non-replaceable dog teeth (syncro teeth). The teeth that are replaceable cost almost as much as a G96 gear, and are only available aftermarket. While the G96 dog teeth are included for free from the factory. But it is no fun having the expense of replacing a gear pair because the syncro teeth are worn out but welded on.
I really like the G50, just trying to help explain the G96/G86 option. The supply & demand equation on the G50's is not good, while the supply & demand on the G86/G96 is a lot better.
Some of the 996 Carreras are putting as much as 350 hp through the stock G96. Ultimately the G86/G96 probably won't handle as much power as well as a G50, but it will be interesting to see if the aftermarket or builders can work any of those issues. Note however that the normal G50 was used on a car that only made 220 to 280 hp. It was only the G50/50 which went above 400 hp from Porsche, and as you all know there are very very few out there. They are hard to find, expensive to buy, and expensive to maintain. It is easy to think of a G50 as a G50/50, but that is incorrect.