This is the forum for helping you out if you're stuck or if you want to discuss the nitty gritty details of the dungeons within Mount Grimrock. Warning: forum contains spoilers!
I read that assembling the machine makes it impossible to go back to the earlier dungeons and therefore impossible to get missed secrets.
Is 66 good or have I missed something? I did compare with maps etc. after completing every level, so I would think I have everything, but I am not sure.
when you are ready to assemble the machine (meaning you killed the monsters on level 12 and you've got the 4 parts in your inventory), you should have found ALL secrets (71) and 5 out of 7 treasures!