Problem with Title

[cirencester]

A friend and I jointly owned an Airstream, but the title was in hs name. It was registerd in Oklahoma. I moved to Oregon, and he gave me a letter saying the Airstream (at the time in Oregon and inoperable) belonged to me. This was some years ago, and it has remained on my property. I had it repaired and would now like to sell it. However, efforts to get him to respond (I'm not sure where he is) have been unsuccessful. Does anyone have any suggestions about resolving this? Could I even claim that the unregistered vehicle has been parked on my property for a number of years, it's abandoned property, I need to be reimbursed for storage fees, and thus need to sell it, some combination of the above??? Thanks for any help.