[MikeS100]

Having said that though, realistically how often are you going to need to know the temperature of the gearbox oil? The only time it's ever really needed is when you're towing, for normal driving it will never get to the point that you need to keep an eye on it. For the time and effort involved in fitting the temperature gauge I think you'd be much better off getting an OBD2 reader that will show live data and just have it connected when you're towing.