I've never been in the vicinity of one of these cmp sensors, I know it's at the back of the engine and mine doesn't leak so I've stayed away from it.
I belive there is infor in the facts pages for removal and installation
for this part. I've read the info so I know it's there, You may try to take it out clean the part and go to yor freindly Volvo dealer and get the right bolts to replace the ones that didn't fit along with what ever seal there may be used in that location also.
If you have read any of my other posts, I'm a beleaver in this stuff
Called auto-rx. The stuff will renew seals and help stop all sorts of small oil leaks. Reach them at WWW.auto-rx.com
Good luck
c roberson