Bear in mind that a Diesel box is no stronger than a normal one, just has higher ratios. Depends on money, if you can afford it, you can get the boxes rebuilt using the MK5 bearings, as they are slightly beefier, but I think you have to change a lot of other internals as well, so probably not cost-effective. I know the Rapid-Fit bloke @ the Ford dealers I used to work in looked @ this method, would have cost over £1k in bits @ staff rate.

Or easier, just find another box and run that. Remember though, if the bearings have gone / are going, then the LSD diff probably ain't gonna be that healthy anyway.

Probably best to have a word with Paul @ North Yorks RS Spares. He probably has hundreds of them holding up the foundations in his place.