A friend has a 2003 103 CI... he is losing oil to the tune of a quart in 500 miles. There is no sign of oil burning. No sign of mechanical leaking ie; cases, lines etc. He brought to his mechanic and he replaced the rings but did not true the cylinders... no change in the oil loss. The bike has plenty of get up and go. It also has an oil cooler... He does not have and oil temp gage... so he wouldn't if the bike was running hot. Can the oil boil and evaporate? Can the oil be burned off in a way that won't show any external signs such as smoke?

Appreciate any input!
Phil