I rebuilt several of the HA boxes, the layshaft needle rollers were the weak point. In fact I have one I rebuilt earlier in the shed !! Rebuilding is like a chinese puzzle, the layshaft gear had to be laid in first, then after the rest was back together you could put the actual layshaft through the layshaft gears, if you were very careful then the needle rollers did not fall out, otherwise you started again. The trick with those boxes was not to fill them with EP oil , they needed (and were specified) straight 90. The ep additives caused excess wear on the bronze bushes and early failure of the thrust washers and then the layshaft needle rollers got the swarf and they failed, taking the shaft with them, I have several worn ones I still use as drifts.