The mount close to (A1) in the picture is prone to breaking for a number of reasons on these cars. My fix is first to get the tab alloy welded back on. Then have a band 50mm wide and at least 8 mm steel thick bent up to strap over the lower mounts (B). Bend it so under final tightening the bracket is pulled tight onto the steering box mounts (that is with the bracket sitting over the lower box mount, there should be a 3 mm gap between the underneath of the strap and the steering box tab on one side, that is taken up by the final tightening of the strap) this should end up looking like (F1). The strap that covers the lower mounts of the box, I recommend as the easiest of the two designs to make and install with the steering box still mounted in the car. The (F2) 3 point bracket is an improved version that is easiest made up with the steering box out of the car as it is a bit trickier. However, it is worth spending the extra time. A press etc at a small engineering firm and a piece of 2.0-2.5inch pipe to form the brace over, will make the job easier. (A2) shows this 3 point brace in position.
Then a plate should be made (8mm thick (C) )that is placed underneath the mudguard that covers the mounting points of the box as fitted in picture (D). Be sure to remove any underseal before placing the reinforcing plate (C) into position.
You will need to use longer grade 8 bolts and nyloc nuts for the final tightening and remember that these nuts should only be used once.
(Thanks Ulf in Sweden for the photo)