Wow that is what I call a thread resurrection!!
Valley pan leaking is not visible as the coolant can evaporate or leak out through two drain holes at the rear of the engine and onto the bell housing or maybe even be inside it as when I removed my transmission there was coolant stains inside. The coolant manifold or water pump pipe O rings are also right at the rear of the engine. But the pressure test mentioned would help diagnose
I would imagine the OP has long got rid of his RR but may be of use if someone stumbles across this. The above is referring to the 4.4 petrol.