see if they have a combustion leak tester similar to this
http://www.ebay.com/itm/like/3323665...=ps&dispItem=1

You leave radiator cap off, and plug top with this, with the blue chemical in the container. if combustion gases blows through it, the fluid changes color (reusable liquid, after putting regular air through it it changes back)

Sounds to me like a cracked head, you wont lose compression numbers from it, it wont start opening up typically until the engine is heated up