So, not being too keen on spending $500 on a new cover, I started looking harder for options to re-waterproof it.
There's nothing much out there recommended for PVC, but I did see a few options for other materials - mineral turps and silicon mixed together, and there's another one with bees wax, linseed oil turps.
I decided to give the first mix a whirl - Selleys roofing silicon and Mineral turpentine mixed at a ratio of 1:3. Give it a good shake, paint it on and away you go.
I did a small section to start with, and it looked good and didn't do any damage, so painted the whole lot last night. Looks and feels very waterproof, so should be fine for at least a couple of years.
Total cost about $17 for a tube of silicon, a litre of turpentine and a paint brush
Aaron