I am using Royal Purple Synchromax, and for me it took about 2 Liters.. I did the differential with it and also used RP. Since both fluids looked like dirt and there were a lot of particles, I decided to buy some extra of each and first pumped some extra fluid in both get some of the particles out, fitted the plugs, drove the car for 15-20km changed the fluid, then another 15-20km and changed again.
Results were noticeable and both felt less notchy and more responsive. Especially transmission, with new fluids car performs better in winter cold and summer hot much better.
Thats my experience anyways..