Peter I think your C43 will have a gearbox oil cooler/radiator. Most of the AMG models do. It is a very small radiator in up near the engine rad generally. Both of my previous models have had them.
I'll ask the technician at Mercedes;
The Plus 8 and all S4 Aeros have a small heat exchanger that uses the engine water to cool the ATF fluid. It is, on Tarka, mounted under the N/S wing, just above the suspension upper arm.
