Charles:~
This link should take you to a "how to do it" - the pictures have disappeared but it is still a descent guide
https://www.volvoforums.org.uk/showt...ght=flame+trap
The job is a little fiddly but quite straight forward with no great problems- when I done my car (same model as yours) the parts just needed a light clean, this included the catchment tank. You may also find that the flame trap itself has been removed, common practice now to leave it out.
All parts are accessible without removing the manifold.
If you have a manual then it is also covered etc.
The oil build up is a likely cause of the crank case ventilation needing a service.
With a little luck all existing parts can be cleaned and reused:
Nothing to be afraid of- give it a go.
Good luck.
Regards Bob.