I've got a R380 stumpy from Ashcrofts on my 90 and I fitted it with an oil cooler(ok-yes even though I live in the Uk, as I do-do some towing and sometimes don't hang about when I'm driving), after spending the thick end of £1200.00 I want as much protection that I can get, I've change the oil every 6 months and it's been as good as gold, I've had it on my truck since 2013 and done about 15-20k miles since then,
The oil cooler is the standard thermostatic block from land rover that fit's onto late LT77's and all R380 boxes, I've fitted it to a 13 row 235mm long-unbranded oil cooler in a vertical position with 1/2" hydraulic swaged pipework run up to the front and it sits next to my full width intercooler, I've also fitted an "oil cooler" from rocky mountain spares to my transfer box as I replaced that at the same time as my main gearbox, Since I've fitted both of these to my truck I've noticed a drop in the engine temperature(on the gauge) and a much cooler cab area too
John