Good Day

I am in possession of a vehicle that was sent to me by the owner for repairs. I have spent a very substantial amount of money on this vehicle, which is now in full running condition. I now have this vehicle for the past 10 months. I have been trying to get a hold of the owner for the past 6 months but have been unsuccessful. I contacted a family member of his, but was told that she does not want and involvment in this as she also has personal issues with him. I went to his home address only to find out that his property has been sold a few months ago. I spoke to his previous neighbour and was told by them that they are also trying to contact him but have had no success in doing so over the past few months. They also have a vehicle of his in their yard.
What can i do as i need to very urgently recover the money that i have spent repairing the vehicle.

Thanks