How do you reclaim the original reg if you do not know it, the current owner has not yet said he knows it.
Its easy pay 5% import duty, not a huge amount, as it could be 20% if a more modern car. The value declared could be different to actual sale, there could be some wriggle room there.
It is being re imported by a different person who originally exported it, might be different if it was the same person.