hi, its only a problem on 2 counts
firstly it must have been repaired properly, if that's been done then no dramas,
secondly if your planning to keep for a good while, then its also not a drama, only if you bought to re sell.
FACT, there are thousands of cars on the road (and I bet a good number of Porsche's) that have sustained heavy damage, and been fixed, but not on the register, so who knows.
I have just bought a 60 plate 997 gen-2 turbo that is a cat B (flood damage) and its a peach, 98% fixed now, just carpets to be put in.
then all the Vosa tests etc, and re apply for the V5.
I have owned 4 cat D cars, and they are no dramas, its normally cosmetic damage, you are aware that it can affect the resale price, but if she is a keeper, then don't worry, enjoy your car.
strange that he spent the money so quickly.......... but as he is a private seller there is nothing you can do, unless you can prove he knew the history, try talking to the last keeper and see if he sold it to this guy and made him aware? you can also contact the
Insurance coy, and see when it was categorised (HPI check will also tell you this) and see if it was during the sellers ownership? a little detective work may turn up some ammo, and then you can go the small claims court on line route.
good luck sir.