90k, using oil 1 to 2 qts between oil change, no smoke, no leak, what could be?

Hello, most manufacturers - as crazy as it may seem - would suggest that a quart every 1000 - 1500 miles consumed is "OK". As a result I wouldn't suggest anything other than monitoring and filling your oil as needed between oil changes. Nothing else makes financial sense; valve guides and piston rings that could be causing larger than desired oil consumption are not easy or inexpensive things to resolve.