It's not an issue if replaced with standard shocks, that is if the fuse has been pulled to stop the pump. Many cheapskates have fitted the non self levelling shocks, to such an extent that every Elite I see...I test the rear suspension to check.
You also need to check the cembelt history, it MUST be changed every 40,000 miles or 4 years...whichever's sooner. So even if it's done 1000 miles in the last four years, it'll need to be done.
Take the expansion cap off after it's stood for a bit after a run and see what you can smell, hopefully not much.
Chris' suggestion of paperclipping is excellent advice, that will alert you to any stored codes.
I know many people describe their vehicles as 'excellent runners' where they're not at all. If a paper clip test reveals, for example, missfire codes that can be a good bargaining point.
Check the rear arches, I've never had an Omega with even a hint of rust there, but some facelifts do have a fair bit of rust...due to poor bodywork care.