I have scoured the 991.1 GT3 owner's manual and cannot find reference anywhere to a 'differential' fluid change maintenance interval, and only see a PDK clutch fluid interval and the PDK transmission oil?
The PDK clutch fluid was changed at 18K miles.

 

Reviving an old thread, but what's the general consensus on the best 75w90 for the diff? Typically I'd go with any high quality diff oil, and planned to buy Motul gear 300, but I'm kinda scarred by my old cayenne with PTV+ and the fact that it only liked genuine porsche (or whoever makes it)
on Pelican the Porsche brand is only $10 more per quart, which I'm willing to spend, but if Motul or Liqui-moly is better, then I'll go that route.

Running in a modified 991 tts.. around 850whp