Whining bearing noise noticiable from about 40mph especially when deaccelerating so no engine noise, gradually worsening, driving normally & gearbox functioning normally. After a lot of ruling things out the noise has been isolated to the gearbox/front differenitals. This was done by running the car at 50mph up on a ramp at my local audi specialist. Noise lowers in tone as car slows and is not related to engine speed (does is in neutral).
He says impossible to locate precise location of noise just by listening, poss bearings in differential (not too expensive to repair) or otherwise somewhere else in gearbox. He is reluctant to start changing differential bearings straight off as if it is not that then its a waste of money if a new gearbox is required as they come with new diffs as well. Anyone had anything like this or any idea on the precise location of noise or tips on where to start?

Current plan is for him to take a sample of oil from both front diffs & gearbox (assuming they don't share the same oil) to see if it is obvious which section has the failing bearing.

Worse case senario is a new gearbox, from audi about £2,800 for the part plus guarantee. Or a reconditioned gearbox but less guarantee or a second hand one (but may have other problems!).

For a 2004 car done 110,000 miles is it worth spending for a new gearbox? Noise is not obvious enough for a part exchange dealer to notice yet, but a new car with similar capabilities is more than a new gearbox?