Has my gearbox melted down ?????

[WAYNE'S X5]

Hi, I've a 2001 4.4i (80,000 miles) and the gearbox has just gone into fail safe mode (meaning stuck in auto in 4th and reverse only) but keeps swithching back to normal ever now and then ? I have checked gearbox oil and it is black and burnt ! my mate read the fault code for me and it reads FAILED PRESSURE REGULATOR has anyone else had this problem and is there anythink that i can do apart from replacing the complete box !!! BMW say new box £3000, my nearest trusted gearbox specialist quoted £1700 for rebuild !
Any info would be great.........
HELP.