Wait, Toples..you said it reads the Install Disk, but not the Workbench disk, right? All you need to do is send that original Workbench disk to another user who also has the original, and get him to fix it for you. Maybe there is a user close to you (? MrZammler) who can do it, instead of you buying new disks.
If nobody else offers, I have original 3.1 disks, and if you send your originals to me in London I will try to fix them for you.
Edit: it would be better to find someone with A3000 disks as mine are A4000T and there are slight differences between the two