Joust a couple months ago, a friend showed me a hydraulic manifold from a Cat tractor or excavator or such. This was a machined cube block of aluminum about 8" on a side with holes drilled in it to form the manifold. It had a leak no one could find. After my friend got it, he pressure checked it over and over and finally located the leak along a perfectly straight line. It turned out to be what is called a "cold lap". It was formed during the process when the plate was created from ingot. It was very tight and invisible to the naked eye.