ford galaxy 95 2.8 automatic transmission oil in to water problems ???

My mate has got a problem with trans oil gettting in to the engine coolant system. There is a small hose in to the top of the "top up bottle" which seems to be dribbling the oil in to the water and then we think that the pressure is blowing the oil out of the overflow pipe in to the under engine wind/dust tray.
The heater matrix has just been replaced, could this have any bearing on the problem?? Transmission losses all drive afer approx 300 miles. There does not seem to be a trans cooler in the bottom/side of the radiator??. Is there a aftermarket cooler available for this model as i am used to American cars and have always installed seperate coolers for the trans to make them last.
Any advice on this would help as he is due to be going over the water soon.
Chris.