Just to clear some things incase people want to know: If a vehicle is subject to a total loss claim (Cat ?) at the very bottom of the VT5 under special notes It may say the vehicle has suffered a 'total loss claim' (not in all cases though!). The only definitive way to find out is a HPI check... Any car that is damaged and claimed for through insurers will be assesed on cost to repair, against book value of the vehicle it has nothing to do with the type of damage (water, fire, accident or hammer etc). A car can have sustained major damage and not be recorded as CAT anything if it never goes to insurers. In the same respect a car can also have relatively minor damage and be written off by insurers as a CAT D (depending on cost to repair against the book value of the car). A good example of this would be a car thats had it's seats slashed!
One thing is for sure due to the risky nature of purchasing a car that insurers have deemed 'non economical to repair' (CAT ?) the value of that car on the market is greatly reduced (however good the repairs are) mainly due to it being harder to re-sell on after purchase. I don't know that there is a specific 'mark down value' my guess is that the value greatly depends on the individual cercumstances.
In my opinion you will be hard pushed to sell that type of car for that price as most people looking for one of these will have done their homework and seen similar cars for similar prices without the looming CAT D label, and you can't sell it without making the buyer aware as you could be prosecuted for that!
So in short it looks like you have a wicked car there with a label thats making it hard to sell. My thoughts are, drop the price if you 'really' want to sell it (by at least a grand I recon) or keep it if you can't bare to part with it for less than you think its worth!
Just my advice on it (as I have been where you are)
Good Luck