[hockenheim]

OP, if I understand correctly during / after the auction the key(s) was (were) stolen. That means they are "out there". If it were me I'd go with the suggestion of re-keying the car with a different set of keys (and lock cylinder / locks) given that some posters suggest the cost is the same as obtaining a new existing key. It just seems too easy in this day and age for someone to figure out who bought the car and their address and then take the car. Call me paranoid but I absolutely can't sleep if I know keys for something of mine are "out there".

Best of luck.