1999 International 4900 with DT466E Oil Usage...help please

Truck has 300,000 miles on it. It uses 1 to 1.5 gallons of oil every 200 miles. No smoke. I use Rotella 15W40 oil.

I have tried the following:

1. Checked fuel for oil, there was none.
2. Checked coolant for oil, there was none.
3. Checked turbo for oil and fan movement, no oil and fan ok.
4. Checked vacuum line from air filter to air compressor, line clear.
5. Changed oil and put Lucas oil treatment in as directed.
6. Changed air filter. Drove the truck about 70 miles...

1999 International 4900 with DT466E Oil Usage...help please

1999 International 4900 with DT466E Oil Usage...help please