tonight i got my 1971 volvo AQ170 started finally and ran it for awhile with the muffs on and then proceeded to drain the water from the cooling system and when i opened the one that is the lowest one in the back there was some oil in the water. I know enough to know this is a problem just not sure how big of a problem. cracked block? let me know your thoughts and how i can check this furthur to figure out problem and how serious. thanks for replies.