Finally found and solved the wet carpet problem.
Without my normal waffle – it was the drain tube from the Air Conditioning. This is a rubber hose with a semi-sealed end with a cut/slit or burper opening. The end was blocked, or had sealed itself shut, apparently a common problem with older Cayennes that have heavy AC use. So, after driving around with aircon running, the cold condensation builds up and has no where to drain to. It sits in a little overflow tank until it finally fills up and floods out on drivers (and passengers feet) when cornering. Sound familiar? If so, then this video will help fix it.
It’s a simple job – one screw look for the hose, found it, opened it, sprayed some lube (WD40) to stop it sticking shut again and *boom* aircon is properly draining and no more wet carpet.