Based on Molakule and Jim Allens' advise in past threads I changed the rear diff fluid early in my new Buick TourX. It uses the GKN Twinster differential with has the ability to send 100% of torque to either axle with computer-controlled clutch packs. The Focus RS uses the same diff and 75w-85 and friction modifier. It still uses Dexron LS in the diff and CHF-11S in the actuator system. The car just turned 6000 miles and based on some issues some are reporting on forums I tackled it myself. There is no service interval on either fluid, and no drain for the CHF11. Capacity is listed at .92qts and fill until it drains out of the fill hole. It was extremely easy needing only one tool, a 10mm hex wrench. The rear sway bar is close to the fill plug so I had to break out the trusty Craftsman ball-end hex wrench and it just fit. The fluid didn't look bad for 7k miles but the drain plug magnet was pretty maxed out. I refilled with Castrol 75w-90LS from a past AZ clearance(good to have a stash) and will report back if it doesn't get along with the clutches.