The rotary cupboard and locker catches on older Eribas are not the cleverest design. There is a built in flaw that means the chances of winding up with an acorn nut in one hand a sheared catch in the other are all too high.
However, repairing these is quite easy and certainly easier than finding replacements.
You need a small hacksaw, a fine drill - 1.5mm or 5/64" - a screw - I use a 15mm x 3mm tapered screw and a cup washer with a 5mm hole - these are easily available in DIY or hardware shops.
Withdraw the knob from the rest of the catch.
Cut off any remaining thread - there'll be just a small stub - make sure you cut square and flush with the square end of the catch.
Locate the centre of the square end and make a small starter hole with a sharp pointed instrument. Check it is dead centre. If so then drill down 18mm (a bit of tape round the drill will act as a depth gauge).
If you look at the photos you'll see that the square end of the knob does not go all the way through the body of the catch. So when the original acorn nut was tightened it puts that joint under tension as it is pulling the knob through the catch. The action of the catch actually bends the shaft very slightly each time and so eventually the shaft shears at the point of greatest tension.
By using a tapered screw with a cup washer that has a 5mm hole, the tapered head of the screw protrudes below the washer and takes up the gap at the end of the shaft. This means you can snug up the screw - do not overtighten - and the shaft will still be free to rotate without the sideload. The cup washer ensures the screw head does not pull through and helps the catch work smoothly.