These engines are a bit notorious for various problems - if you have a look at HJ's reviews sections, plenty of detail there. The engine was also used in the Vauxhall Vectra and Saab 9-3.

Unless you know what you're doing, I'd sugest you need a garage to get on it - as said, it's a common engine, so absolutely no need for a main agent, just a decent indie or (ideally) a diesel specialist. Once again, HJ has the good garage guide, and plenty of customer reviewed places also on places like goodgaragescheme.com - a local indie in my area is rated incredibly highly on there, and plenty of reviews generally too.