gary1 - you can either have a 12 year overhaul which means at the end you will have 12years/2200hours remaining. Or 12 year inspection which is entirely different. So say the machine has 800 hours remaining (that would be the minimum hours I would recommend for the inspection) once complete you will have a machine with 12 years and 800 hours remaining.
I know a company in Europe who will do fixed price inspection for not a lot (excluding any parts found requiring replacement and finite parts such as blades...which in your case are fine). The frames will need to be removed and inspected no matter what you do.