my son had a landrover freelander which had a neat little cooler mounted under the left front guard with its own thermo fan
That's what happened to my 2007 2.2 Hdi. Hatchback The idiots that owned my car before me put a bypass loop on the exchanger and a loop on the cooling system. I took the bolt out last weekend and the fluid was a browny colour. The replacement unit I got is the wrong one, it's too short and the locating lug is at 2 o'clock. I drove this car for a week and everything was operating within manufacturer's specs.The gearbox is not a "poor choice" its the bean counters that skipped fitting any decent oil cooling.The only ones to have dedicated cooler were 605 and XM.That silly heat exchanger only heats oil further and also it perforates silently dumping coolant into trans oil and that is the end.I have developed adapter and have fitted oil coolers to several AM6 and ZF 4HP20s.That is the smartest thing you can ever do.The valve body does not get cooked in boiling oil and lasts longer.Temp drops from 90+ deg C to 60.I use a very high thermal efficiency cooler,fit stainless steel mesh inside bumper and flush the oil 100%.