Popstar,
I wouldn't waste good money.
The original owner has to keep their contact details up-to-date by law.
When aircraft registration is transferred, usually the new and old owners fill in the back of the registration document. However, it is not unknown that this is missing etc etc.
In that case, the CAA write to the registered owner and lets them know someone is trying to change details. They sometimes, nowadays, follow this up with a phone call.
So.
First, why did original owner not respond to CAA requests. If they didn't, then some sort of statute of limitations must apply. Not sure if it is the short or long one.
I take it someone noticed they didn't "own" the aircraft anymore. If it was in their farm shed, they might have spotted it wasn't there. If it was on an airfield, they might have noticed no parking or hangerage charges.
If you "own" it, maybe you are responsible for 10 years parking!
And if no paperwork to prove sale price, loan agreement (you can use it as long as you pay the costs etc) or "gift", then who knows what has happened.
Not worth the candle, I'd say.
I know the statute on unacknowleged debts is seven years, if that is a help. Land is 10/12 years.