Repair to your local haberdasher and procure a metre of shearing (sp?) elastic for the princely sum of 15p or so. Cut two 44 cm lengths.
Prise out the two guides from the parcel shelf 'tube' and separate the two halves of each.
Remove traces of old elastic from each cord, and attach new pieces by binding with thread and blobbing some PVA glue on to make sure they do not come off. Leave to harden.
Make a loop in the other end of each elastic, and push a piece of wire through the tube, using this to pull the first elastic back, holding the end of the cord with a clothespeg or similar so it does not pull through. The loop goes on a projection inside the half-guide - feed the other cord through in the same way, and clip the guide halves together so the elastic emerges through one hole, the cord through the other. Repeat for other cord.
ZX Parcel shelf cords
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