Unfortunately if the work is carried out without an insurance company being involved, there is no way it can be traced, and certainly won't appear on any HPI or vehicle check.
Is the previous owners details on the log book? If so try to make contact.
Just say, it's come to light that a repair has been carried out at some point, and ask which garage performed the work. You can then see if that bodyshop offer any kind of warranty on their work
Might be worth a try
