Is that true? if so, any one know that temperature I should do it at?
I find it difficult to believe that the gearbox capacity will change much with temperature. Bentley recommends driving a few miles before draining, I think more to suspend the sediment in the oil than for temp, same reason as engine oil. It's more important that the car is level.
I drove to lunch then back before my change, 20 mins total, oil was warm when it came out, not hot. It takes a while to get the car jacked and the under-cladding off. I let mine drain over night, as I felt it was important to get as much of the old oil and sediment out (and I changed to RP Synchromax.) I overfilled it a bit and waited for the excess to stop draining/dripping before buttoning it up (about 15 mins.) I replaced the bottom plug, but reused the top one, I wanted to be sure the drain plug didn't leak or fail.
Well worth doing, my car had 63K mls and the shifts, esp. into 2nd, are MUCH better. I'll probably change at 30-40K intervals now.
Update: I changed the Sychromax out for Redline ATF, the smooth shifting with Sychromax did not last.