Maintenance technicians at John Day Dam estimated 63 gallons of oil spilled into the Columbia River from a pinhole leak in a turbine guide bearing chiller discovered on Monday.  According to a statement from the U.S. Army Corps of Engineers, Portland District, the leak was discovered near the downstream side of the dam.  The Corps says staff isolated the system, began identifying the exact number of gallons lost and started fixing the issue.  Operations Division chief Dwane Watsek says the turbine guide will be out of service until it is repaired.  This is the second spill at Corps dams on the Columbia River this month.  The Dalles Dam spilled 45 gallons of oil into the river on December 3.  Corps technicians originally estimated the impacted turbine could have lost up to 200 gallons, but they confirmed the lesser amount on Friday.