We've been going through this with our Lightwing. It is a factory built, so available for training & hire. However the engine, although low hours, is now years expired. This means it is "on-condition" which requires annual inspections and the aircraft can't be used for training or hire, or fly over populated areas. There are costs to have L2 inspections and I believe there is a RAAus annual fee.
19 registered is amateur built, not just because the engine is "on condition"
We have someone who wants to buy it and do alterations - things that normally require Engineering certifications (as it is factory designed & built). To get around this - and this isn't for everybody as it is a lot of work. Transfer the plane to the new owner using the RAAus Tech Form 028 - Damaged/Unairworthy aircraft acquisition which takes the aircraft off the Register then do the work required making sure that it is equivalent to 51% built (dismantle, recover, engine work etc) and re-register it in the 19 category. Once in 19 you can run the engine "on condition" provided you have a plan for monitoring and maintaining it. Determining the 51% is up to RAAus, and 51% is a lot of hours and work, and expense. Fortunately for us, and the plane, this is just what the buyer wants to do - a comprehensive inspection, renewal and rebuild. Document and photograph as you go to prove the extent of the work.
The alternative is to have the engine overhauled to renew its life. A quick call or email to Tech at RAAus will get you a better answer. @bauple58 I am assuming it is a RAAus registered.