We never saw temps higher than 104°C when we tested an ATB with 391 bhp to the rear wheels . In fact 99.9% of the time, was spent well below that and in double figures. For our application, we then decided it wasn't necessary to fit a cooler. Don't forget that the only heat generated is by the shearing effect of the gears, there is no temperatures being put into the oil like with an engine.

Feel fee to put one on, but I would monitor your temperatures first, as I think you will find that you would need to get on loose surfaces for the temps to rocket for a cooler to be required on a Cossie.

Also, I use a top quality fully synthetic gear oil such as Mobil SHC, which is rated to a lot higher temps than I ever saw...