faulty transmission temperature sensor for 911 Turbo S PDK on 2011 Porsche Cayenne Turbo

Under modest driving in a 2011 Turbo S with PDK, red transmission overheat light occurred. Dealer believes problem is a faulty temperature sensor in PDK and not a mechanical problem. However, dealer says that sensor cannot be replaced.

I assume they checked the fluid levels and they are OK.
In some cases software could cause the problem also, so make sure the latest update was installed.
If the sensor is not available as a single unit, the entire PDK transmission has to be replaced. The warranty should covers it.

Do you know if the sensor is available as a single unit? The dealer thinks not but is likely looking for ways to avoid replacing the whole PDK. Should I accept it if they tell me that, in the future, if I see the temperature overheat light, I should simply ignore it??