If your basement is immediately behind the rwp location, see if the brickwork is damp. Unless it goes down to the same level as the bay foundations (which go down to basement level I believe?), then leaks from this may not have an effect on the bearing soils.
However, as it's cast iron, it's unlikely to be completely watertight and it would be prident to replace it in plastic flex-jointed pipe, regardless.
Although the cause is not immeidately obvious from the info posted, the movement to the bay is of a low order and, at this stage, it's not worth undertaking more extensive investigations, or getting a professional firm in to have a look-see. I would suggest repairing the cracks, either by stitching in of similar bricks, or cutting in helibar across the crack/s, putting some expamet over the area of repair, making good to the plaster and redecorating. That way, it can self-monitor as any significant reopening would suggest the possibility of further movement and the need to undertake more extensive investigation at that time.
Perhaps Woody can call round one afternoon, after doing some beam calcs, a survey or two and before answering damp questions...
