Excellent write up of how to get to the oil trap:
https://www.volvoforums.org.uk/showthread.php?t=71672
I did it a few years ago with the help of these instructions and it was quite easy. I do not have EGR which made life a bit easier. On the other hand, I do have an inlet manifold with four additional LPG injectors to make access more difficult. No need to take the manifold completely out, just unbolting it from the head is sufficient.
I removed the oil trap basically to fit a new gasket underneath (original one had hardened) and found the trap itself was still clean, even after 300K+ miles. Thanks to a lot of motorway driving, LPG and good quality oil maybe?