2000 SL2 DOHC engine using oil

I assume you are changing your oil every 3,000 miles. Vehicles with high mileage well burn a little oil. If you are changing it every 3,000 miles 2quarts is a bit excessive.
There are some oil leaks that only happen when the vehicle is on the road and you may not notice it. Inspect under your car very closely for any signs of oil leaking.
Just because there is no smoke coming out of your exhaust dosnt mean your motor is not burning oil. It may be burning sufficiently in the combustion chamberm that you dont see any smoke. Do a compression check on your cylinders so you have a better ideal of whats going on.