Is it possible to get a pic of the area to show the extent? I haven't see it on dattos, but one of my other loves are mopars, and aussie ones had the steeringbox on the chassis rail not on the front k frame, and over the years they either crack or rust (or both) and the steering box tears away completely if left long enough. As such there's a bunch of tech info and options with regard to diy repair, and most valiant places are very skilled at this sort of repair work. I know that sounds odd, but it might not hurt to ask a place like that to take a look at it.

Often the outward 'damage' is the tip of the iceberg and internally the rail can be rusted a lot further in each direction - starting from the inside and working it's way to the outside (visible) surface. And sometimes it's not cheap to fix either, as they have to cut out the entire damaged/deteriorated section, replace that and potentially run a 'sleeve' over the outside and weld that on to regain full strength and safety.