The A/C compresser has a clutch on it so you aren't actually turning the compresser when the A/C is not turned on.Brian Elfert
Detroits tend to leak a little around the sharp edges. At your mileage and low oil loss I wouldn't worry about it foranother 100,000 miles or if something big happens. If you get to 5 gallons per 1000 miles I would look for a leakif it isn't burning the oil and making smoke. The extra lubrication on the back of the bus helps make it easierfor air to flow around there. Keeps the airstream lubricated and tail gaters back a little farther. On the issue of a/c belts.. I just used a razor knife and zapped them off, that way I didn't have to remove the blowerbelt.
Normal "full" position on the dip stick is one inch (1") below the engine block/oil pan interface.Check to see if yours is accurate - mine wasn't! HTH. . .